Macs during System days were as closed as modern Apple devices, and stuff like A/UX were more of an experiment than anything else.
The reverse acquisition of NeXT brought some UNIX culture into Apple, but even then, Steve Jobs always saw it as a checkbook item, a detail to make NeXTSTEP relevant in the UNIX workstation market.
Apple saw it as a survival mechanism to get out of their crash course.
Now that they are better than ever, they can happily go back to 1990's way of working.
An important difference is that classic MacOS didn't actively scare users away from installing apps outside a centralized shop controlled by Apple (which didn't even exist back then).
Had Copland been better managed, not even OpenGL would ever got a place on it, rather Quickdraw 3D.