Folk music is music that people create to amuse themselves. And people never really "create" anything, they really borrow from here and there and mold it to fit the moment. The "selling out" process really is just molding the music to amuse a lot more people, and fit a lot more moments.

The thing is, at that point, you've made a choice to stop having a good time, and to concentrate on making other people have a good time. More profitable, but less interesting.