That's the unfortunate modern trend. The web folks that move fast and break things love living on the bleeding edge, and create strong pressure for everyone to keep up, and that the answer to library compatibility is "wait until someone complains, fix the direct reason, cut a new release, and let the dependents fix their own code".
You still have to find someone who both wants and can maintain them. That's not always a given.
And also, why? If I donate to the PSF, do I really want my money to go into the maintenance of ... checks notes ... MacOS 9 path manipulation functions (https://docs.python.org/it/3.7/library/macpath.html)?
Just because you're well-funded doesn't mean you get to spend money on useless things. And most of the python community would consider this useless. Nobody even made a pypi copy of it.
None of this explains why python has the need to drop modules for the standard library.
They claim "nobody is maintaining them"… but they are well funded and can easily afford someone to maintain them.
I think at the core they don't care about backwards compatibility, but instead of doing it all at once like with python2/3 are now doing it little by little, creating a python4 without calling it so.