Re: I'd love to know the rationale...
"...behind this decision by Apple. I mean even Microsoft was able to keep compatibility with 32 bits apps, FFS!"
People like Microsoft because they keep tons of legacy code in their OS in order to keep backwards compatibility with programs written 30+ years ago. People like Apple because they don't. Realistically, it's difficult to argue that either is objectively better. If you rely on old code, MS is obviously the better choice. If you don't, there are clear benefits from avoiding all the legacy bloat and associated bugs and quirks that come with it.
The only company really at fault here is Adobe, who might be cynically trying to push people into paying them even more, except they didn't even manage to get the new versions working properly.