What I think most people don't think about... Often literally refuse to think about... Is the real consequences of the potential actions. Sure, he could have sex with all of the "extra" species women, but what if some of them don't want to share? How negatively would they react? How much of a living hell would they make everyone's life until he was kicked out to try and return the peace?
Relationships are extremely rarely so simple as sharing nicely. While it IS possible, it takes a certain kind of person, or a certain set of people, for it to work smoothly...
(Heck, even some "harem" hentai don't have an exactly "happy end" for the male protagonist... As he literally becomes a sex doll for the females...)
Consequences, people, consequences...
Besides, completely ignoring the interpersonal relationship(s) between those on and off the farm, how long do you think the local government would allow it to continue before exiling the "extra" species women back to their homes? And the federal (Japanese) government, to exile extra species women from Japan for potential endangering their men (needless to say public morals)... Even those who are uninvolved... And then the rest of the human world?
No... He would become the most infamous man on Earth if he fell into temptation... Consequences...