If the market was actually open, people would compete on different cuts and the % would eventually drift towards whatever the right number is.

Epic seems to do just fine charging 12% on their PC games store, vs Valve's variable (maximum of 30%; lower for big rich game studios) cut on Steam.

Apple and Google have also both put in place a lower cut for independent developers, which is further evidence that 30% isn't the 'right' number. It's just a number the market has no choice but to put up with.

I certainly don't blame them for wanting to pocket 30% of the filthy billions of dollars kids and gambling addicts pump into stuff like Genshin Impact. That's free money for Apple.