Board Thread:General Discussion/@comment-28365753-20170322105059/@comment-31336039-20170322110947

In the game "Monster girl quest paradox" They give the biological explanation. (different universe, different rules but still close and largely inspired by MGE)

Because if Male Monster exist, they would fertilize human female, and she will be knock for nine month. When a human male is always more or less ready to go. So if they were to much new male monster humanity would be in danger of extinction. "So monster girl raping human male is not a threat to humannity survival."

Maybe the scientifical explanation to why there is no male monster, in addition to your own theory and why no monster lord try to change that fact. Humanity's extinction = Mamono's extinction.