How come in a lot of TV-MA 아니메 they give female characters nipples, but not males?

No I am NOT trolling! This has been bothering me for a while, but I really don't see why they don't give male characters nipples if the MA rating allows female nipples to be shown and it's not like men don't have nipples.

EX: Berserk, Devilman, Bio Hunter just to name a few
Exceptions (that aren't porn): Akira