It is more than that, I really like openbsd as a desktop system. This is niche enough that I have zero expectation for any sort of support from the hardware vendors. However, because the amd drivers are opensource. Heroic people in the obsd dev community are able to make it work there. I don't strictly need a gaming gpu for my desktop work, but it is nice to have a setup I can boot linux on to play games with.

Heroic because the amdgpu driver is strangely huge, more code than the rest of the obsd kernel combined, It has something to do with gpu's having no isa stability and the generated code for each card present in the driver.

Perhaps more importantly, AMD enables others (community, Valve, etc) to do the work themselves when they have different priorities from AMD.