why is it so hard for girls to dump their bfs?

I just dont see why wud girls take mistreats from their bfs , n stil they wonder, shud i leave him what shud i do? like what the hell is wrong with girls?? some self respect n dignity wudnt be bad...I understand that girls specially teenagers like to hang out with the bad boys n stuff but if they're bein treatd bad why wud they stil stick around??