From what I've read, the offshoots of the pelvic nerve (at least I think that was the one are arranged differently for every person with a vagina. So some people have more nerve endings in the clitorus, vagina,perineum or anus. While for vaginas the nerve endings are arrranged very differenty, in penises there is much less variation. So the difference in where someone has the most nerve endings kinda explains why some people like or don't like penitrative sex anal stimulation et. etc.