I'm not sure I fully understand your question. Are you asking why abuse gets passed on from generation to generation?

I think normalcy prevents young victims to have awareness that their reality is abusive. They adopt both survival instincts and learned behaviours that they then forward on as adults without realizing their behaviours are dysfunctional and abnormal. They are then drawn to other dysfunctional people for comfort. Many people are afraid of the unknowns so if you were to pair up a dysfunctional person with a healthy minded one, they're not going to know how to relate with them.. or may even be afraid to.

I'll stop there because I don't think I'm answering this correctly.. and maybe I'm not saying very much at all.