Short version: AMD as a company is dysfunctional. Perfectly happy to throw away $300Mil on failed acquisition, unwilling to hire sufficient number of competent driver developers.
Where did you get this idea from? Just because a patch set got rejected, we can dismiss the fact that AMD had been providing excellent open source driver support for years, and just call them incompetent?
AMD is prioritizing the business here, which makes perfect sense. Why would they spend more money than necessary to appease the Linux maintainers in order to serve the tiny population of Linux gamers who probably don't give a crap about how the kernel is maintained? Their business is on Windows.
Neither AMD nor Nvidia develop Linux drivers for Linux gamers. Not that they don't pay attention to us with fixes and optimizations here and there, but a good part of that is games simply being applications that make use of a lot of driver functionality that might not receive enough testing otherwise.