Self-loathing, misogyny, spite, far right ideologies... and out of feeling hard done by/entitled, they find solace online where they can trade ideas and blame women, people in relationships, society etc.
It's a movement that would probably be less prominent pre-internet times. And like every movement, it will have factions. But also, it's not a membership card carrying organisation.
There's a lot of them over this side of the world. Thankfully they tend to stay online, rather than act out their agenda.