The reason why ASIC resistant POW algorithms do not actually exist.
It was never impossible to make ASICs for coins, but it has to be a good business to build them / buy them.
There are 2 directions nowadays:
1. ASIC resistant coins that after some point get mined by ASICs or become worthless. It still takes long until ASICs are designed for them..
2. Coins that change algo from time to time to make it become bad business to invest in ASICs.