How did I purge most of my installed packages when trying to free space in /boot

Question

I've been getting messages that my /boot drive was running out of memory. So, in order to make sure I could keep updating my machine, I tried to remove unnecessary files. I followed a procedure given here: How do I free up more space in /boot?, which was to to this:

dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d' | xargs sudo apt-get -y purge

When I tested the first part of this command, I got the following reasonable result:

root@Bedrock:/boot# dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | 
sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ 
]*\).*/\1/;/[0-9]/!d'
linux-headers-4.4.0-28
linux-headers-4.4.0-28-generic
linux-headers-4.4.0-77
linux-headers-4.4.0-77-generic
linux-headers-4.4.0-78
linux-headers-4.4.0-78-generic
linux-headers-4.4.0-79
linux-headers-4.4.0-79-generic
linux-headers-4.4.0-81
linux-headers-4.4.0-81-generic
linux-headers-4.4.0-83
linux-headers-4.4.0-83-generic
linux-headers-4.4.0-89
linux-headers-4.4.0-89-generic
linux-image-4.4.0-28-generic
linux-image-4.4.0-77-generic
linux-image-4.4.0-78-generic
linux-image-4.4.0-79-generic
linux-image-4.4.0-81-generic
linux-image-4.4.0-83-generic
linux-image-extra-4.4.0-28-generic
linux-image-extra-4.4.0-77-generic
linux-image-extra-4.4.0-78-generic
linux-image-extra-4.4.0-79-generic
linux-image-extra-4.4.0-81-generic
linux-image-extra-4.4.0-83-generic
linux-libc-dev:amd64
linux-libc-dev:i386
linux-signed-image-4.4.0-77-generic
linux-signed-image-4.4.0-78-generic
linux-signed-image-4.4.0-79-generic
linux-signed-image-4.4.0-81-generic
linux-signed-image-4.4.0-83-generic

I could also see:

root@Bedrock:~$ uname -a
Linux Bedrock 4.4.0-87-generic #110-Ubuntu SMP Tue Jul 18 12:55:35 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

So, I knew I wouldn't be reoving any of the 87 files, which I was using. Although I did wonder why I had headers for 89 files? Shouldn't be an all or nothing situation - either headers, images, extras & signed images for 89 files or nothing?

But, my real question is why did I end up removing most of my installed packages, when I followed through with the full command. Some of these packages were still very much in use - e,g, g++, libboost, opencv etc. Luckily, the output enabled ne to see just what I had that needed to be reinstalled:

root@Bedrock:/boot# dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d' | xargs sudo apt-get -y purge
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  bbswitch-dkms cdbs cm-super-minimal dh-translations dkms gir1.2-gst-plugins-base-0.10 gir1.2-gstreamer-0.10 gir1.2-gtk-2.0 hdf5-helpers icu-devtools intltool lib32gcc1
  lib64ncurses5:i386 lib64tinfo5:i386 libaec-dev libasound2-dev libboost-atomic1.58.0 libboost-chrono1.58.0 libboost-context1.58.0 libboost-coroutine1.58.0
  libboost-graph-parallel1.58.0 libboost-graph1.58.0 libboost-locale1.58.0 libboost-log1.58.0 libboost-math1.58.0 libboost-mpi-python1.58.0 libboost-mpi1.58.0
  libboost-program-options1.58.0 libboost-random1.58.0 libboost-regex1.58.0 libboost-serialization1.58.0 libboost-signals1.58.0 libboost-test1.58.0 libboost-timer1.58.0
  libboost-tools-dev libboost-wave1.58.0 libboost1.58-tools-dev libc-dev-bin libc6-i386 libcairo-script-interpreter2 libdapserver7v5 libdbus-1-dev libdmx-dev libdmx1
  libeigen3-dev libepoxy-dev libfs-dev libfs6 libgeos-dev libgfortran-5-dev libgif-dev libgl2ps-dev libgssrpc4 libgvc6-plugins-gtk libharfbuzz-dev libharfbuzz-gobject0
  libhdf5-cpp-11 libibverbs-dev libilmbase-dev libjansson4 libjbig-dev libjs-sphinxdoc libjs-underscore libjsoncpp-dev libkadm5clnt-mit9 libkadm5srv-mit9 libkdb5-8 libllvm3.6v5
  liblzma-dev libmircommon5 libmircookie-dev libmircookie2 libmircore-dev libnetcdf-cxx-legacy-dev libobjc-5-dev libobjc4 libopencv-gpu2.4v5 libopencv-ocl2.4v5
  libopencv-stitching2.4v5 libopencv-superres2.4v5 libopencv-ts2.4v5 libopencv-videostab2.4v5 libopencv2.4-java libopencv2.4-jni libopenexr-dev libpciaccess-dev libpcre32-3
  libpcrecpp0v5 libpixman-1-dev libqt5concurrent5 libraw1394-dev libraw1394-tools libreadline-dev libreadline6-dev libsndio-dev libssl-doc libtiffxx5 libtinfo-dev
  libtinfo-dev:i386 libudev-dev libvtk6-java libwayland-bin libwayland-dev libwebp-dev libwebpdemux1 libxaw7-dev libxcb-shm0-dev libxcomposite-dev libxcursor-dev libxdmf-dev
  libxdmf2 libxdot4 libxinerama-dev libxkbcommon-dev libxkbfile-dev libxmuu-dev libxpm-dev libxrandr-dev libxrender-dev libxres-dev libxss-dev libxtst-dev libxv-dev libxvmc-dev
  libxxf86dga-dev linux-image-generic linux-signed-image-generic nettle-dev nvidia-prime nvidia-settings python-attr python-autobahn python-concurrent.futures python-lz4
  python-mpi4py python-msgpack python-pam python-pyasn1-modules python-scour python-serial python-service-identity python-snappy python-trollius python-twisted python-twisted-bin
  python-twisted-core python-txaio python-vtk6 python-zope.interface python3-brlapi python3-louis python3-speechd qt5-qmake qtbase5-dev-tools screen-resolution-extra tcl-vtk6
  thermald x11proto-bigreqs-dev x11proto-composite-dev x11proto-dmx-dev x11proto-dri3-dev x11proto-fonts-dev x11proto-present-dev x11proto-randr-dev x11proto-record-dev
  x11proto-render-dev x11proto-resource-dev x11proto-scrnsaver-dev x11proto-video-dev x11proto-xcmisc-dev x11proto-xf86bigfont-dev x11proto-xf86dga-dev x11proto-xf86dri-dev
  x11proto-xinerama-dev xbrlapi xserver-xorg-legacy
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  gir1.2-gtk-2.0 libdrm-amdgpu1 libdrm-amdgpu1:i386 libdrm-dev libdrm-intel1 libdrm-intel1:i386 libdrm-nouveau2 libdrm-nouveau2:i386 libdrm-radeon1 libdrm-radeon1:i386 libdrm2
  libdrm2:i386 libegl1-mesa libgbm1 libgl1-mesa-dev libgl1-mesa-dri libgl1-mesa-dri:i386 libgl1-mesa-glx libgl1-mesa-glx:i386 libglapi-mesa libglapi-mesa:i386 libgles2-mesa
  libgtk2.0-0 libgtk2.0-bin libllvm4.0 libllvm4.0:i386 libpulse-mainloop-glib0 libpulse0 libpulsedsp libsensors4:i386 libwayland-bin libwayland-client0 libwayland-cursor0
  libwayland-dev libwayland-egl1-mesa libwayland-server0 mesa-common-dev pulseaudio pulseaudio-module-bluetooth pulseaudio-module-x11 pulseaudio-utils
Suggested packages:
  lm-sensors:i386 pavumeter pavucontrol paman paprefs
The following packages will be REMOVED:
  bazel* build-essential* comerr-dev* doxygen* doxygen-dbg* doxygen-gui* doxygen-latex* g++* g++-4.8* g++-4.9* g++-5* gfortran* gfortran-5* gnome-orca* graphviz-dev*
  krb5-multidev* lib64ncurses5-dev:i386* libatk-adaptor* libatk-bridge2.0-dev* libatk1.0-dev* libatspi2.0-dev* libblas-dev* libboost-all-dev* libboost-atomic-dev*
  libboost-atomic1.58-dev* libboost-chrono-dev* libboost-chrono1.58-dev* libboost-context-dev* libboost-context1.58-dev* libboost-coroutine-dev* libboost-coroutine1.58-dev*
  libboost-date-time-dev* libboost-date-time1.58-dev* libboost-dev* libboost-exception-dev* libboost-exception1.58-dev* libboost-filesystem-dev* libboost-filesystem1.58-dev*
  libboost-graph-dev* libboost-graph-parallel-dev* libboost-graph-parallel1.58-dev* libboost-graph1.58-dev* libboost-iostreams-dev* libboost-iostreams1.58-dev*
  libboost-locale-dev* libboost-locale1.58-dev* libboost-log-dev* libboost-log1.58-dev* libboost-math-dev* libboost-math1.58-dev* libboost-mpi-dev* libboost-mpi-python-dev*
  libboost-mpi-python1.58-dev* libboost-mpi1.58-dev* libboost-program-options-dev* libboost-program-options1.58-dev* libboost-python-dev* libboost-python1.58-dev*
  libboost-random-dev* libboost-random1.58-dev* libboost-regex-dev* libboost-regex1.58-dev* libboost-serialization-dev* libboost-serialization1.58-dev* libboost-signals-dev*
  libboost-signals1.58-dev* libboost-system-dev* libboost-system1.58-dev* libboost-test-dev* libboost-test1.58-dev* libboost-thread-dev* libboost-thread1.58-dev*
  libboost-timer-dev* libboost-timer1.58-dev* libboost-wave-dev* libboost-wave1.58-dev* libboost1.58-dev* libbz2-dev* libc6-dev* libc6-dev:i386* libc6-dev-amd64:i386*
  libcairo2-dev* libclang1-3.6* libcuda1-367* libcuda1-375* libcv-dev* libcvaux-dev* libdap-dev* libdc1394-22-dev* libegl1-mesa-dev* libexpat1-dev* libfontconfig1-dev*
  libfontenc-dev* libfreetype6-dev* libgail-common* libgail18* libgdal-dev* libgdk-pixbuf2.0-dev* libgles2-mesa-dev* libglib2.0-dev* libgraphviz-dev*
  libgstreamer-plugins-base0.10-dev* libgstreamer-plugins-base1.0-dev* libgstreamer0.10-dev* libgstreamer1.0-dev* libgtk-3-dev* libgtk2.0-dev* libhdf4-alt-dev* libhdf5-dev*
  libhdf5-serial-dev* libhighgui-dev* libhwloc-dev* libicu-dev* libjpeg-dev* libjpeg-turbo8-dev* libjpeg8-dev* liblapack-dev* libmirclient-dev* libmircommon-dev*
  libmysqlclient-dev* libncurses5-dev* libncurses5-dev:i386* libncursesw5-dev* libnetcdf-dev* libnuma-dev* libopencv-calib3d-dev* libopencv-contrib-dev* libopencv-core-dev*
  libopencv-dev* libopencv-features2d-dev* libopencv-flann-dev* libopencv-gpu-dev* libopencv-highgui-dev* libopencv-imgproc-dev* libopencv-legacy-dev* libopencv-ml-dev*
  libopencv-objdetect-dev* libopencv-ocl-dev* libopencv-photo-dev* libopencv-stitching-dev* libopencv-superres-dev* libopencv-ts-dev* libopencv-video-dev*
  libopencv-videostab-dev* libopenmpi-dev* libpango1.0-dev* libpcre3-dev* libpng++-dev* libpng12-dev* libpq-dev* libprotobuf-dev* libprotoc-dev* libpulse-dev* libpython-all-dev*
  libpython-dev* libpython2.7-dev* libpython3-all-dev* libpython3-dev* libpython3.5-dev* libqt5opengl5-dev* libsdl2-dev* libspatialite-dev* libsqlite3-dev* libssl-dev*
  libstdc++-4.8-dev* libstdc++-4.9-dev* libstdc++-5-dev* libtiff5-dev* libtool* libvtk6-dev* libxerces-c-dev* libxfont-dev* libxft-dev* libxml2-dev* linux-generic*
  linux-headers-4.4.0-28* linux-headers-4.4.0-28-generic* linux-headers-4.4.0-77* linux-headers-4.4.0-77-generic* linux-headers-4.4.0-78* linux-headers-4.4.0-78-generic*
  linux-headers-4.4.0-79* linux-headers-4.4.0-79-generic* linux-headers-4.4.0-81* linux-headers-4.4.0-81-generic* linux-headers-4.4.0-83* linux-headers-4.4.0-83-generic*
  linux-headers-4.4.0-89* linux-headers-4.4.0-89-generic* linux-headers-generic* linux-image-4.4.0-28-generic* linux-image-4.4.0-77-generic* linux-image-4.4.0-78-generic*
  linux-image-4.4.0-79-generic* linux-image-4.4.0-81-generic* linux-image-4.4.0-83-generic* linux-image-extra-4.4.0-28-generic* linux-image-extra-4.4.0-77-generic*
  linux-image-extra-4.4.0-78-generic* linux-image-extra-4.4.0-79-generic* linux-image-extra-4.4.0-81-generic* linux-image-extra-4.4.0-83-generic* linux-libc-dev*
  linux-libc-dev:i386* linux-signed-generic* linux-signed-image-4.4.0-77-generic* linux-signed-image-4.4.0-78-generic* linux-signed-image-4.4.0-79-generic*
  linux-signed-image-4.4.0-81-generic* linux-signed-image-4.4.0-83-generic* mir-client-platform-mesa-dev* mpi-default-dev* nvidia-367* nvidia-375* nvidia-opencl-icd-367*
  nvidia-opencl-icd-375* python-all-dev* python-dev* python2.7-dev* python3-all-dev* python3-dev* python3-pyatspi* python3.5-dev* qtbase5-dev* r-base-core-dbg* r-base-dev*
  tcl-dev* tcl8.6-dev* tk-dev* tk8.6-dev* ubuntu-desktop* uuid-dev* xorg-dev* xserver-xorg-dev* zlib1g-dev*
The following NEW packages will be installed:
  libllvm4.0 libllvm4.0:i386 libsensors4:i386 libwayland-bin
The following packages will be upgraded:
  gir1.2-gtk-2.0 libdrm-amdgpu1 libdrm-amdgpu1:i386 libdrm-dev libdrm-intel1 libdrm-intel1:i386 libdrm-nouveau2 libdrm-nouveau2:i386 libdrm-radeon1 libdrm-radeon1:i386 libdrm2
  libdrm2:i386 libegl1-mesa libgbm1 libgl1-mesa-dev libgl1-mesa-dri libgl1-mesa-dri:i386 libgl1-mesa-glx libgl1-mesa-glx:i386 libglapi-mesa libglapi-mesa:i386 libgles2-mesa
  libgtk2.0-0 libgtk2.0-bin libpulse-mainloop-glib0 libpulse0 libpulsedsp libwayland-client0 libwayland-cursor0 libwayland-dev libwayland-egl1-mesa libwayland-server0
  mesa-common-dev pulseaudio pulseaudio-module-bluetooth pulseaudio-module-x11 pulseaudio-utils
37 upgraded, 4 newly installed, 235 to remove and 66 not upgraded.
7 not fully installed or removed.
Need to get 40.3 MB of archives.
After this operation, 2,940 MB disk space will be freed.

Perhaps this will teach me not to use the -y option when piping commands into apt-get purge, but I still don't understand what happened here. Why didn't I just lose the old linux files?