I already told you: prestige. There is no profit motive, despite anything to the contrary you might have heard from the FBI or BSA. Occasionally people will enter the scene looking for ways to make money but this kind of motivation is seriously frowned upon and the individuals in question are often publically scorned. Simply: you don't earn any rep from being a conman or petty ripoff artist.

Here is a little more context: Most release groups consist of individuals who break copy protection for fun. They compete amongst themselves to create clever hacks and one-up each other. It's a very tightly knit tribal culture: me and mine vs you and yours. Cracking releases or moving releases from one top site to another becomes an interesting game and so too are the metagames and scene politics that surround it. For example: a courier might strive to get friendly with site admins or group leaders who are privvy to upcoming "pres" (or pre-release) so they can get a leg-up on the competition. Be among the top 10 traders on a site for a few weeks and suddenly you have a reputation: you get invited to trade on more prestigious sites, join more prestigious groups and generally pal around with community elders. You develop very strong bonds over time and that's what keeps you in: the scene is where your friends are, it's where people know and respect you. Plus, the competition to be the best can be intoxicating.

What gradstudent said. For the prestige and respect. It's a rush, addicting and exhilarating.

Topsites can offer a pay to leech scheme. It's often a hushed topic and people don't like to talk about it (because it is insecure). Many topsites are at it.

A lot of scene members react badly to topsites like this, and often people infiltrate such sites and public a "scene notice" about them containing siteop nicknames, hostnames, IRC/FTP details, and screenshots.

Scene notices are like the news system of the scene. They allow people to publish messages that will disseminated to all the other scene topsites.

I imagine it's satisfying to help people and feel recognized (via group affiliation) for it.