Their rage needs to vent, so they use verbal and emotional abuse as a way of expressing this rage, but they direct the rage at people who have nothing to do with the reason for the anger. Many times abusers create situations which allow them to explode. But, most abusers probably try to avoid thinking about what they do. If they think about it too much, they may have to acknowledge that they are behaving badly and then they might have to change. No one likes to feel they have to change, and even small changes are difficult to manage.
Abusive behavior requires a great deal of time, energy and persistence.
Not many abusers change. Even those who know that what they do is wrong, manage to convince themselves that it is necessary, or that they were provoked, or that the victim deserves the abuse, or some other justification. Abusers are complicated as are the causes of abuse. You might want to read some books on the subject and learn more about the whole issue. Helps explain the different perspectives of the victim and the abuser.