There are plenty of reasons artists license their music for a rhythm game. There's money, certainly, and notoriety. But what about scorn? For Billy Joel, it was more than enough reason to license a dozen or so of his songs to Rock Band 3. Here's his account from USA Today:"I've never allowed my music to be used in a game before," but an Entertainment Weekly review of NBC's The Office changed his mind. Alluding to an episode in which characters mention a Rock Band featuring Billy Joel, "the critic wrote something like, 'God forbid that ever should happen.' So I called my people and said, 'Get me (on) that Rock Band game.' Then I wrote the critic, saying that every time I get a check, I'll give him a little nod."
We're assuming the songs will cost money, but we'd submit that reading the above story and knowing we'll never do anything remotely that cool is a dear enough price to pay.