When I think of folk music, I think of the long refining process a song goes thru by means of the oral tradition. These songs have survived, not just because antiquarians love to study obscure subjects, but because the tradition lives. When you like a song well enough to learn it, and then well enough to perform it in another's hearing, and if they love it well enough to learn it, it keeps on. The songs that last are the ones that mean something to people thru time. Who knows what of the mish-mash of musical styles prevalent now will stand the test of time. A folk song lives not just because someone stands to gain financially but because it strikes a chord(!) in enough people for it to survive.