There is a lot of "free" music but very little actually free music (almost all of it is under a license that prohibits use in pornographic content), and even less that is not A) crap, and B) overused.There is a lot of free music, why not use it?
Trust me, I've done a LOT of research into all of this, and using licensed or free music is basically out of the question. This is a hot topic among us adult game developers (we have several private threads about this topic on this forum alone) and several of us have opted to solve the problem by going in different directions than what everyone used to do just a few years ago.
In my case, I've chosen to compose my own music for my next game, Supermodel. While some of the music in Long Live the Princess would be okay to use (mostly the stuff added towards the end of its development), the majority would still need to be replaced. I would like to compose my own tracks for this purpose, but it's not something I can prioritize for the time being. Maybe later.