Lack of enforcement doesn't mean the rule doesn't exist. Basically the porn games are in the position of playing Russian roulette. Sure they might last a while but what happens if they get successful on itch then get yeeted? Or the money gets put on hold pending arbitration? All sorts of fun things that this dev is choosing to avoid by the simple metric of avoiding the stated rules.
Anyway the itch policy changed sometime last year and some developers noticed and altered their stuff... some didn't, or chose to gamble. But it is what it is