There are liberally millions of app, Apple can't expect all of them to be always up to date on day one, to even sw like postgres. You can't just change the semantic of an API, it's just wrong. Apple should introduce a new API, deprecate the older one and remove it two or three versions later minimum. They just don't care until people is going to buy their hw.
Traditionally, Apple does not guarantee total ABI stability. They push betas instead to allow people to fix the issues, and then support older releases for multiple years.
Yes, unmaintained software might or might not stay fully functional on macOS for long, but that's not an Apple priority.
