It's the same stuff any number of software applications do on their install programs.
They try and push the "extras" or the "paid" trial, etc,etc. Often they use clever wording
and/or tricky screen layout to steer the install their way.
Does Avast get a commission if some of those extras are installed? As I said, I don't blame Avast,
they're not doing anything unique.
This is one reason I will never install through the GUI; it's not quite clear what "extras" will creep in,
if any. I always do a clean, custom install, so i can clearly see all the options.
Usually I deselect all the extras.