Having done similar (not identical) things at that age, a lot of it is quite literally for the LOLs, and more than a bit is for community identity.
Fame: Non-existent, since you don't tell people.
Money: Non-existent, you don't get paid.
In retrospect, I think a major drivers for teenagers for a lot of activities is a sense of identity. You feel like one of the role models in [name your favorite hacker movie]. It's the same reason why punks wore spikes and mohawks, goths wore black, and people might pick a genre of music (even if privately). I'd guess a lot of more negative things, like vandalism, are similar too.
You become part of a community too.
And ultimately, you contribute to it. As much as it might be illegal, cracking software helps other kids who can't afford that software. Few real engineers will use a hacked copy of AutoCAD, and literally everyone I know began to pay for music once they could afford it. On the other end of the bell curve are kids who can't afford those. Providing them with access is a community service. And it's going up against The Man. It's illegal, but by the code of ethics we followed at the time, it was very ethical.