Is there financial incentive for them to bother?

One thing they should've learned from Nvidia is that it's really worth it for them to invest making their devices function as broadly as possible. Crypto and AI waves both benefited Nvidia much more than AMD partly due to their devices being more universally usable.

That "partly" was worth hundreds of billions of dollars but AMD were cheap/shortsighted enough to hire a few dedicated engineers.

Perhaps not but one of the great things about Nvidia is their latest drivers often support very old cards.