Fun fact; ESRB rating is not a law, its just an advisory rating, a guidance.
Fun fact: Most store enforce ESRB ratings for appearance only, to appeal to the parents into shopping and buying games for their kids. To create a family friendly situation where the parents have no concern over their kids forking out cash over the counter.
Fun fact: You can still sell your games without ESRB ratings, its just that a certain stores would refuse it. But it is still not illegal to sell non rated games!
Reminder that almost all adult/hentai games on Steam does not ESRB ratings, or any ratings whatsoever.