I agree; however, engine developers are already dedicated to building massive behemoths of software that is the game engine and they constantly do collaborate with driver devs, essentially sharing much of the same skillset.

Also, the onus is actually on the GPU manufacturers (not game engine devs) to simplify the programmability of the GPUs to the level we have for CPUs (we also do not write microcode, however, the programmability is much much simpler with access to good compiler toolchains). This will massively help non game engine developers who need GPUs for other kinds of compute.