The controversy mostly arose in the early '60s with celebrity performers like Burl Ives, the Kingston Trio, and Peter, Paul, and Mary. They and others had originally been singers of modernized versions of traditional songs, and were marketed as "folk singers" and "singers of folk music."

When these artists branched out into recent, pop-like material, they still were marketed as "folk singers," and what they sang became "folk" by definition.

Years ago I posted a quote from the music critic of the prestigious "New Yorker" magazine, who called a composer of radically experimental music a "folk musician," apparently because her compositions she didn't fit into any mainstream category.