This was partly explored in Erich Fromm’s work “Escape from Freedom” and “The Anatomy of Human Destruction”, but basically, if I understood correctly, sadistic personalities use it as a means of defence against loneliness and isolation. By exerting power over another, they temporarily lose the painful feeling of being alone. Abusive people tend to be miserable when their victims leave them and they have nobody to control.
Nobody gains anything from cruelty, it’s a symptom that something’s terribly wrong with the person in the first place. Even animals don’t display acts of cruelty in the wild, they do so only when confined to cages and subjected to other inhumane treatment.
This was very depressing to learn. I know a lot of software engineers, some of them PhD students, who are really smart and clever people, able to abstract concepts, form connections in thought, recall relevant information and make intelligent conclusions every day. And then they say things like masks don’t do anything during COVID, the vaccines don’t work, Russia is defending itself, the wokes are oppressing everyone and destroying everything etc. It’s almost impressive to see someone seemingly intelligent act like the lowest Trump supporter with certain topics like someone just flipped a switch.