Why apt can't upgrade some packages?

Question

I have many Ubuntu Desktop 22.04 instances installed through either direct installation or VirtualBox. All of them installed in the same way. Sometimes and for few of them happens the following:

#1
sudo apt update
...
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
26 packages can be upgraded. Run 'apt list --upgradable' to see them.
#2
sudo apt upgrade 
...
#3
sudo apt autoremove
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded. <-----
#4
sudo apt autoclean
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
#5
sudo apt clean

Observe in #3 the following part:

0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded

Question

• Why apt can't upgrade some packages?

If is re-executed almost the same process happens the following (Observe #2 because is new and #3 because has more details)

#1
sudo apt update
...
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
3 packages can be upgraded. Run 'apt list --upgradable' to see them.
#2
apt list --upgradable
Listing... Done
libsmbclient/jammy-updates 2:4.15.13+dfsg-0ubuntu1.6 amd64 [upgradable from: 2:4.15.13+dfsg-0ubuntu1.5]
libwbclient0/jammy-updates 2:4.15.13+dfsg-0ubuntu1.6 amd64 [upgradable from: 2:4.15.13+dfsg-0ubuntu1.5]
samba-libs/jammy-updates 2:4.15.13+dfsg-0ubuntu1.6 amd64 [upgradable from: 2:4.15.13+dfsg-0ubuntu1.5]
#3
sudo apt upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
Get more security updates through Ubuntu Pro with 'esm-apps' enabled:
  imagemagick libopenexr25 libmagickcore-6.q16-6-extra libmagickwand-6.q16-6
  imagemagick-6.q16 libmagickcore-6.q16-6 imagemagick-6-common
Learn more about Ubuntu Pro at https://ubuntu.com/pro
The following packages have been kept back:
  libsmbclient libwbclient0 samba-libs
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded. <---
#4
sudo apt autoremove
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
#5
sudo apt autoclean
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
#6
sudo apt clean

Note in others instances not always appears the following part

• Get more security updates through Ubuntu Pro with 'esm-apps' enabled:

Therefore it happens randomly and even in few instances of Ubuntu Server. If my memory does not fail me, I had this experience for Ubuntu 18.04 and 20.04 too.