Because women generally have better lives than men in almost every aspect. Sometimes drastically. In humans, males carry the heavy loads and burdens while females have pleasure handed to them in a golden bottle; (their only real role in procreation and thus the human agenda is to become pregnant, males do everything else, so females are otherwise free). This is forced by both biology and society. Especially biology, as women are significantly happier even in countries where they're treated like shit. It ultimately comes down to male disposbility. Extremely unfair, but nature favors what wins, not what's good. And what wins in this world is usually evil.

Look at the trans stats too. Notice how most are MtF but nearly all the detransitioners were FtM. Everything points to the grass being much greener on the female side.