[willvarfar]

The GPU has many cores but they are organised in groups that share the instruction cache and decode logic, so they all execute the same program in lock-step (AMD call these 'wavefronts' and NVIDIA call this 'warps').

A many-core RISC-V has many independent cores, all with running their own cache and decode logic so all able to run different code and stall independently of each other.

There are problems beyond graphics where warps or wavefronts are great matches, and for those problems GPGPUs are very effective. But there are also problems where, even if each core is basically running the same program, cores can diverge and for that you want cores with their own decoders so they can stall or branch independently.

Its all a tradeoff.