I think Apple is afraid of the AI people switching to CUDA and neglecting Apple's own accelerators. Whatever the case is, it's entirely petty - Nvidia still ships FreeBSD drivers and would probably gladly pick up Apple support again (at least for CUDA drivers).
If it was as simple as "Nvidia was an unreliable hardware partner", they wouldn't go out of their way to arbitrarily limit the drivers you can run.
Apple’s icy relationship with Nvidia started right around when CUDA came into existence and before Metal ever existed. Nvidia created tensions between Apple and Intel and later handed Apple the headache of a class action lawsuit by knowingly shipping faulty GPUs.
I think Apple Silicon and Metal vs CUDA might have been a strategic reason for not repairing that relationship but that came years later.
I guess now that they have the infrastructure for these more niches OSes, it's not too hard to just keep going (especially if the kernel APIs are relatively stable).
