I like to think of the old Grand Theft Auto: San Andreas situation that allowed a mod to enable player to rail their g/f in a player scene instead of behind the scenes that set an example in the industry, and why anything that could affect ratings is spelled as prohibited behavior.

It was like a sex emote in a scene. ESRB immediately changed GTA's Mature rating to Adults Only, game was pulled from retail shelves, got banned Australia right away, among so many downstream problems and civil lawsuits. Rockstar left the assets in the game because during development they intended to push boundaries but sided against such and only disabled it, allowed mod developer to basically re-enable it.

Ratings do really matter because the Federal Trade Commission keeps a close eye on ESRB stuff, and pushing into AO territory is a death wish.