They've had the best 3D drivers on Linux for years. There were issues with Optimus and Ion but IIRC a lot of it was legal and issues with Linux's driver infra back then meant it required far more effort than it was worth at the time.

Their drivers might work, but saying to users "here, load this giant blob with a history of privesc bugs into your kernel" isn't what I'd call "supporting Linux".

Meanwhile, AMD are active contributors to Mesa and DRM, which benefits everyone.

I wish they'd open things up too, but it's there prerogative, and Linux repesents a minuscule share of their market. The fact that they support it in the way they do today is surprising.