Tab completion does not work for some commands

Question

I've followed Tab completion doesn't work for commands and tab completion of filenames is working for this command:

ls  /home/login/public/ui.<TAB>   

But not working for this command

drush arr /home/login/public/ui.<TAB> 

in $SHELL /bin/bash is there. Mine is completely new install. I've placed this code in the .bashrc:

if [ -f /etc/bash_completion ] && ! shopt -oq posix; then
    . /etc/bash_completion
fi

/etc/bash_completion exists

Tab completion doesn't work for commands