I think reputation is far more important here. They make enough money to drown themselves in it, no need to have bad publicity at this point. Also, there are a lot of people with AMD hardware. Not as many as NVIDIA but they're still relevant. They're a cheap alternative and a lot of people opt for them.
If I'm not wrong while NVIDIA owns a bigger market share AMD still makes up at least 30-40%. It's pretty important to optimise for as many gaming rigs as possible, rather than the newest models only.
I'm fairly sure that AMD owns less than 30% share these days, there is a real risk of it going under which would be bad for everyone.
