Because we're in an unnatural state. The natural state of man is supposed to be in unity with the the female specimen. God created girls to accompany men, it doesn't even matter if he's real or not, it's literally natural human/entity behavior to have a partner. You just think animals just pop up? These reproductive organs aren't for show or aesthetic purposes. They're meant to be used. It's also another reason why a massive portion of incels in general are horny is because they want to reproduce, not a scientist but it's easy to conclude to. Being stoic and stone cold is the worst response you could ever do in this scenario. It's self flagellation thinking that all these emotions are irrational.