Why are narcissists vengeful

Because it makes them "happy" to destroy you.

Inside their warped heads, they think they're actually doing you a favour too.

Tearing you down, stealing all of your money, your home, your car, destroying your finances, cheating on you, lying, etc., it's all a way to strip you down to nothing.

They rationalise this in their warped brains as you learning to "build yourself back up."

They want to play god

Insisting they are God ?

Per the (Narc)

They insist you are going to learn some major Lessons from Them!

And be grateful for The journey

File ancounter claim when they sue you for the lessons …. (Their Cruelty)