I suspect the reason corporations sponsor symphony concerts, jazz, and "new" music is they perceive those genres as "ART" ! Folk music is not an "emerging" art like "new" music, isn't "classical" like symphony music, and doesn't have the "intellectual" and/or politically correct "race" dimensions of jazz. Folk is just folk, too common, too grassroots to be considered worthy. Tis a pity.

The National Endowment for the Arts is a hard nut to crack because espisodes like "piss Christ" ticked off the conservative congressmen and they severely cut the agency's budget. (I work for an Arts org. who once got big bucks from them, now zilch) The guidelines for the National Endowment for the Humanities (as they were explained to me several yeara ago) generally require you to "talk" (or write) about an issue. So they might fund an educational lecture about a certain ballad, or ballad collection, but would not support a straight out concert of those ballads.