On Books: Gloating Villains

Sometimes real life is visibly dramatic, and when I thought about the various complaints directed at fictional villains, I remembered that real-life villains do, in fact, do the things that fictional villains do (that are often considered a writer's ploy.)

Take, for instance, the villain gloating over the helpless victim.   Why doesn't he/she just kill the helpless victim (the hero, the hero's girlfriend, the lost prince, etc) before the victim or the victim's friends can kill the villain?

Because