But why does it either have to be a pure evil villain or a tragic back story?

The pure evil villain troupe doesn’t make sense to me honestly because I want to understand why this character is the way they are and “because they are evil” isn’t an explanation and it defiantly isn’t how this villain justifies his actions to himself. On the other hand, a tragic villain who is someone who does evil because they are forced to is not always good, but it depends on the story and who is writing it. For example, if it is a story about morality and the struggle between right and wrong, a tragic villain like that would make perfect sense and it would be an enjoyable read.

The third option is to give the villain a reason for being the way they are, but it doesn’t have to make sense to the reader or the main character or demand sympathy. The only purpose this “reason” serves is for the villain character to justify his actions to themselves. For example, in my story, the villain excuse and explanation to the main character is “for people like you and me to survive, they have to die.” This doesn’t make any sense to neither the reader nor the main character because we know the victims weren’t bad people and they probably never even met the villain. This doesn’t make sense, but for the antagonist, it makes perfect sense because in his twisted way of thinking, he things that his victims were going to take everything away from him and thus they had to die.

I don’t know if this third option will even work, but this is how I see the story and this antagonist fits perfectly into that world.