Because of the way other programs handled the act of file-sharing -- acting as an intermediary between users, but never actually "knowing" who had which illicit digital tracks -- suing program makers (Kazaa, Gnutella, BitTorrent) becomes more problematic. The RIAA still tries. They fail. File-sharing grows.
In 2003, they start suing kids. Then they sue everyone. They sue grandparents and farmers on dial-up connections. They sue the recently deceased. They've sued over 20,000 people since. They're still losing.
Now, unfathomably, the RIAA has set up a website (p2plawsuits.com) on behalf of labels that allows you to confess your transgressions, pay a discounted settlement and not get sued. They want it to seem like an act of mercy. It's really an act of desperation. Their suits have gone horribly. Each muddy litigation and case of mistaken identity creates precedent that in no way favors the recording industry. Thus, they want to avoid the entire judicial quagmire (hemorrhaging money all the way).
What the RIAA doesn't get is that file-sharing isn't primarily about stealing. It's about ease. You can do anything you want with stolen music. Play it anywhere. This offsets the relative ass-pain of finding and getting it. With legal downloads, the ease is all on the getting end. Once you get it, though, you have to deal with copy protections that stifle ease of use. Right now, for many people, the scales tip toward theft. Fewer restrictions would tip them the other way without question.
I buy videos from iTunes because it's easier to get Veronica Mars there with copy protections than finding unprotected ones on BitTorrent. You loosen restrictions, you empower me, you gain revenue on music, and Illegal p2p becomes a vastly smaller problem. The shortsightedness of the RIAA is such that file-sharing has become the Prohibition of the digital age. Us? We're just moonshining until we can get the hooch we want, legal-like.