what happen when a monstergirl attacks a man but the man knock her down and raped her to show her that he is not so easiely to defeat? maybe she respect that man and want to have him as a real husband and do what he will.
The boobs suck away almost all the speed, most of the little intelligence that they have in the first place and act as a Double-edged sword by inciting men to be raped and acting as a fail-safe to the rape at the same time.