Why would it be? Again, nobody cares.
The GPU makers want to sell you new GPUs, so they don't care. The game makers don't have much of an incentive to cater to whatever percent of the 10% of AMD users are stuck on ancient hardware, so it's not cost effective for them to care. The users are glad to extend the life of some devices, I'm sure, but the narrow band of software and features this enables is just going to get smaller over time as new software comes out, so as a collective the amount of caring will only go down.
Again, you are talking about edge cases. We are considering a blob of several billion devices in a rat race to sell, refresh and upgrade billions more. Linux will grow as it comes preinstalled in new devices, justifying additional support from manufacturers in a constructive loop. I'm not against it serving as a remedial OS to salvage old ewaste at all, but that's not how you turn it into a major player on desktop devices.
Oh, and for the record, I have some 6 series AMD GPUs around the house still. Even with native RT your assessment of their modern viability is... optimistic.