The problem is that OS X is the generative platform
If your "only iOS matters" hypothesis is correct than Apple only cares about generative OSX for generating iOS apps. That means keeping XCode working at all costs, and they can safely ignore every other use. I suspect that they understand that apart from students using Pages to write papers, MS and Google own the office productivity space.
The only remaining code to write are highly proprietary front-ends and the occasional mega-backend.
Have you seen Swift Playgrounds for iOS? I wonder, seriously, if that's not the start of Apple's attempt to put software dev on iOS. No, it's certainly not capable now, but in five years?
If your "only iOS matters" hypothesis is correct than Apple only cares about generative OSX for generating iOS apps. That means keeping XCode working at all costs, and they can safely ignore every other use. I suspect that they understand that apart from students using Pages to write papers, MS and Google own the office productivity space.
The only remaining code to write are highly proprietary front-ends and the occasional mega-backend.