Nowadays, to be successfull in PoW mining you have to be priviliged in several ways:
- have access to 'free' (usually means stolen) energy
- live in a country with low-taxed offshore deliveries or got ASIC manufacturer in your neighbourhood
- win in 'pre-order' gambling game
That may be true for compute-bound PoWs but not for memory-bound PoWs
that need random access to more memory than can be fit on an ASIC.
Thus an ASIC for such a PoW needs to be equipped with (more expensive) memory modules,
and only needs to be optimized to saturate the memory latency, which also limits power-use.
Such an ASIC would also not have much of a performance advantage over a multi-core cpu
running the PoW, since both are limited by memory latency.