If that was the argument they'd have replaced it way sooner, because 3.x came out 14 years ago, 3.4 (when the 3.x branch could be called "actually ready for use

If that was the argument they'd have replaced it way sooner, because 3.x came out 14 years ago, 3.4 (when the 3.x branch could be called "actually ready for use") came out 8 years ago, 2.7 was announced to go EOL "soon" 5 years ago, and was properly killed off almost 2 years ago now. We've seen an entire major version release of MacOS come out since Python themselves went "look, we're killing this thing off, deal with it", at which point Apple should have dealt with it, but didn't. This is a replacement for the convenience of their own staff working on the OS, nothing more. It's good that it's finally happened, but it's a good five years overdue, and there's no motivation beyond "we no longer use it" at play here.