"what is their purpose?is it to promote folk music,or folk revival performers? or both."

I think there's also something of a tautology in the question above: promoting a music is all but inseparable from promoting its performers. Music is, after all, made by musicians.

There's that use of "revival" in the question, however. Which makes me think yet again that all too many of the discussions and heated arguments on this forum stem from the fact that folk is a nebulous term. It simply cannot be defined in the hard-and-fast hermetically sealed way that some posters here are convinced it can.