[ColonelPhantom]

A big part of the reason is that Blender on Nvidia supports hardware accelerated ray tracing using OptiX. HIP-RT exists, but is not used in Blender yet. I think the Intel oneAPI backend for Arc GPUs also misses RT acceleration.

AMD claims to have HIP-RT working internally, but not yet suitable for posting publically. Intel is planning it, I think. Both should land around Blender 3.6, if I'm not mistaken.

If you take the raw FLOPS, CUDA (not OptiX) and HIP are actually nearly equivalent in performance last I remember. I think RDNA2 just does "more with less", at least in terms of gaming performance per FLOP (e.g. due to the huge cache).