For me it was about making a statement.
I had gotten into an argument with a professor on a discussion board. He used derogatory terms to refer to me, which pissed me off. I sent him a virus that was supposed to just damage files and delete some random files. It turns out it propagated onto their main network and crashed the entire universities network.
Suddenly, you feel untouchable (even though the virus had gotten out of control, which I didn't mean it to do). You feel like you can do anything and are beyond the reach of law enforcement. I'd never done anything like that and you felt really powerful, in control. You now had this idea if someone slights you, you have something to shut them down and they can't reach you.
Then the feds show up in your class, bring you to a windowless room on campus you didn't even know existed and start threatening you with jail time while they question you. This happened in the late 90's and the CFAA was still really new and DA's really didn't know how to apply it. I was pretty lucky for sure. The stuff they were threatening me with was like interference with interstate commerce, identity theft, stuff like that. They gave me the old, "You have a bright future kid, don't fuck it up." speech at the end. That was enough to scare me straight so to speak. I lost my campus network access for a year, which sucked, but the whole experience was enough for me to stop doing what I was doing.
It was just in time too, because you saw during the early aughts, the feds really started going after hackers. They started using the broad powers of the CFAA to put some really high profile people in jail with some pretty hefty prison times. To this day, I still look back and feel like I dodged a bullet there.