Actually, Apple did depart from nVidia for a variety of reasons, mostly due to nVidia’s attempt to extract patent royalties that Apple had issues with. You can side with Apple or nVidia on that front although most seem to blame nVidia in this case.
Basically, it’s up to nVidia by itself to make drivers now. Apple is no longer involved. Getting information out of Apple though is a pain for developers. I know one piece of software that’s been waiting for over two (2) years for a final spec on the APFS drive format so that they can update their software and Apple still has not provided it.
So, blame can be on both sides here. Most Mac users would prefer to use nVidia, but AMD seems to work with Apple better and so AMD is the chosen one right now.