Every story has and needs a villain. And of course, every villain needs a motive. Unfortunately, not every villain has a motive.
Giving villains believable motives can be hard, and that's why a lot of writers turn to a cliche I call "strawman chaotic evil": a villain who goes out of their way to hurt the innocent as much as possible, even if it gains them nothing, even if it puts them in danger, simply because "mwahaha I'm evil and I like it". But that's not how real evil works. A real person cannot actually enjoy being evil; instead, everyone who acts evil in real life does so for personal gain. So let's all ditch this trope. We can do better.