He definitely is a super genius mad scientist but he gets credit for omniscience that he absolutely doesn't possess. In-lore you could say that he (or really his team) figured out how to do it for males first and since he was all gas no brakes he just sent it. Then if someone asks why your super incredible trans-human technology only works on half the people you either admit your shortcoming or you say "it's because dudes rock obviously" and pretend you meant to do that.

Again though, the reality is that they thought it would be cooler that way and wrote themselves into a corner way before they realized anyone who doesn't spend their weekends at the comic books store in the 80's would ever see it.