For a lot of people it is an ego trip, or revenge gone rampant. People that destroy windows, usually worked for windows in the fist place. It’s one of those “OKay fine! FIRE ME! You’ll be sorry you did!” Kinda things.
More and more “Mac Viruses” are coming out just because they want to prove they can do it.
When I was in college we got to talk to a “reformed” hacker. He took any contract to write spyware, adware, virus, anything that someone would want to put on your computer… if the price is right. One porn site payed him 30,000$ for an adware. Four days of work, and he got 30,000$. Sure a bunch of preteens and teens had their computers destroyed… but crap MAN! 30,000$!!!! I wish I could do four days of work for that much money.