I expect that there are users, who are not themselves developers, who are using either apps or scripts which rely on the system-installed Python 2. They likely aren't aware that they're using Python, and they may not even know what Python is. It could be one line in one shell script block in one automator action that a coworker put together five years ago.

It's okay for that stuff to break. (I wish Apple would put more effort than they do into making it break less often, but that's neither here nor there.) But, it should break in a major release, when the user is prepared for things to break. It should not break in an update that was installed automatically overnight.