Patriarchy makes us men types see relationships as markers of success in some kind of competition, or boxes to check on the "doing it right" rubric. When a woman rejects a guy like that, they feel themselves slipping back down to where they started, all that progress seemingly lost, and it makes them fucking angry, probably because a guy like that is too emotionally illiterate to not see rejection as some kind of gatekeeper slamming a door in his face (always being able to consult the patriarchy rulebook in times of emotional upset leaves you that way).

Btw this is not to say that these men have no agency or are purely victims. Maybe I am just hoping there's a conclusion to be reached that isn't "men are essentially volatile beings" since I'm a man who has never struggled with that kind of anger and I want to believe I am living proof that there's a better way for men to live.