Well yes, but why should a company like nVidia or AMD make a driver for an OS with a user base that's a rounding error?

Even if they just release all the information required to make one, you still need the labor to write the drivers.

I think what parent is really asking is if there is something like rump kernels[0] for GPU.

[0] is this even a thing anymore? rumpkernel.org seems to have become a generic IT news aggregator.