One reason gpus are not used as accelerators for chess is the host-device latency.

Afaik the latencies are in the range of 5 to 10s or even 100s of microseconds,
so you can get max 200K kernel calls per second per thread,
even if the gpu is able to process its task much faster.

Therefore, Eta v0300, a cpu based AlphaBeta search with gpu as ANN accelerator,
is flawed by design.