Some people just get off on being horrible to people they think are powerless to fight back. It's a power trip that's often addictive for people who naturally have the personality of a bully, and it's definitely something the Karens of the world can't seem to live without.
Case in point: a whole flock of Karens
came to this restaurant and complained about the service for basically no reason. Then they deliberately left a huge mess behind as an act of spite. They probably thought they got away with it too.