Why don't kids with abusive fathers hit them back once they grow up?

I have seen big a teeanger being beaten by his father. I mean the guy was big enough to hit his father back and hurt him badly if he wanted to, but he just took the beating. I have never heard of abused people hitting their fathers back even when they get bigger then their fathers. I have never understood why?

Edit: Wow this blew up. I guess I was wrong, some people do hit back. And I didn't consider the mental trauma the kids go through while asking this question. Thank you all for your responses.