It does seem kind of weird to criminalize it. Obviously cases where abuse is happening or minors are involved should be criminalized, but we already have laws directly for that.
The world at large is in a long and slow ongoing transition from "this is a strict list of what behaviours are permitted in an intimate relationship and this is a list of punishments for behaviours outside that list" towards "consent is the rule, everything is fine as long as it happens between consenting adults".