I think when people feel weak or insecure they sometimes as they seek more control and power over their lives go to the opposite extreme and exert power over others. It raises them up, and puts the other person down in the mind of the bully. These people fail to recognize or understand good relationships are generally on an equal footing, not one person having more power than the other. Young people it is more understandable, because they are still learning, although bad behavior is really never acceptable. In adults it is disgusting.
I know a few people who are bullies in adulthood, and some of them you can actually feel them smiling and skipping away after they treat you like shit (I feel this from women like this). They are a total joke if you ask me, and generally miserable people. Don’t get me wrong, what they do might hurt me for a moment, but then I realize they have to do it, because they feel so crappy about themselves. I know two people who became bullies after going through therapy. The therapists encouraged them to make boundaries, and that became a huge brick wall with little communication. They both basically left their families after being hateful and full of anger and sadness. Neither had abuse in the family, although it was not growing up in the Cleaver household.
I am not a socialogist or psychologist. The above is just my take on some bullies I have witnessed