To understand rollbacks it's better to assume the user has itself borked something rather than the system. You don't necessarily rollback to previous package versions, just to the last state everything was working.

Sure you can fix whatever you did wrong, but that might imply quite a few things and take time. If you go to the snapshot prior to your changes, it takes a lot less time (just a reboot), less guess work, and you can continue working from a blank slate.