The problem is that if you get an ESRB AO rating, no one will publish it, because everyone believes that Adults Only means porn or gratuitous sex. And maybe it does. But it can also mean violence, or mature content, or things which are simply not appropriate for non-adults. I don't think the distinction should actually exist, honestly, but that's a separate discussion.
But the problem is if you consider a game of some sort that has extensive use of graphic violence, then you put yourself directly in line for a bit censorship banhammer.
NC-17 films can still be made. But effectively, AO games cannot, as the market space for it is artificially shrunk through censorship.
So any time you are working on a game, and the violence or sex or maturity of content starts reaching a potential AO level, it gets cut, or toned down.
There are game ideas right now which can never be made, thanks to platform censorship. It holds the industry back.