They were badly hurt early on. Abusive individuals are their own victims. Abusive people can't meet their emotional needs. They think their partner should do that. Victims often are abusive.
Victims sometimes think they are the abuser.
Abuse is just one more framework for viewing relational difficulties that can be seen in other ways as well. Viewing dysfunction through this framework is useful because many people can identify with the phenomenma. Verbal Abuse is not recognized and is poorly understood by the therapeutic community. Note how many of us speak of an emotionally or otherwise abusive childhood. Dysfunctional families produce adults who do not take care of themselves.