Nothing to do with upbringing. They lack the social skills and in most cases, attractiveness, to easily attract the opposite sex. Most you’ll notice really tried in their teen and younger years but when that didn’t pan out their brain essentially created a safe space in their mind where it can’t be their fault. It MUST be women are terrible people because I’m a great person and they don’t want me. Think of it like kids who’ve had a shit childhood. They see the world through a protective lens they’ve created to make their unpleasant reality easier to swallow.