Losing your virginity, sex and reproduction for what I've seen. Monetary back up (not always and slightly more beneficial for women).
The need to put up with other people's shit. Sacrifice your "me" time. Meeting people you don't care about. Being related by proxy to people you don't care about it. Giving up your freedom. Being manipulated in certain way just because otherwise you won't have sex. Discussions, discussions discussions. If married, high probability of divorce.
Some people like just negated into that way of thinking. I'm anti social and aware that I'm not a good person. That doesn't mean that I wanna change. There's a lot of way more awful and disgusting people out there getting laid, why not me?
The fact of life is that some people are just cursed to be alone.
I'm not an incel. But according to modern internet I am because I'm virgin and I'm aware that no women would want to fuck me plus being a loser. I never clawed. There's your answer.