“Successful” does not mean psychologically secure. I know many very successful people, by almost any objective metric, education, income, career status, looks, who are still very insecure about themselves when it comes to romantic relationships. I have no specific knowledge of these sorts of abusive relationships, and if any of my friends have been or are in one they have not shared about it with me, but my understanding (open to correction) is that that emotional/psychological insecurity is what drives the behaviors on both sides of a romantically abusive relationship.
Do you also know people who are successful but insecure?
My guess is that they have a hunger for the romantic approval and that the very inconsistency of its being given, mixed with abusiveness, acts like those variable ratio schedules of operant conditioning protocols, that create behavior patterns fairly resistant to extinction.
Does that make any sense to you?