And I think that's totally reasonable—as long as Apple makes the change in a major update, when users can expect (some) things to break and should be encouraged to make time to prepare.

Part of it is that it's just a mental burden to keep this kind of compatibility information in my brain. I have VMs set up of past macOS releases in case I need to run something old. I don't have VMs set up for earlier versions of a release, and I don't even know where I'd get an installer. Admittedly, in this case it would just be a matter of installing Python, but I don't necessarily know that as a user, or the software could need to be linked to Cocoa or some such.