Perhaps they are afraid of stepping on advertisers toes. Counterfeiting of Art. It's easy to do. We are offered art at least a dozen times a year which we reject because of its questionable province or authenticity. We will gladly proved a certificate of Authenticity on any art we sell, and we believe other dealers who haven't should adopt the same policy.
Folk artist have art stolen from their houses.
Homeless artists frequently have their art stolen. The artists let work go without anything in writing, never to see the art again. Reproducing Art Without Permission. People take folk art and make it into T-shirts, note cards, posters, etc. without getting approval of the artists and without compensating them. Folk artists have the same rights as any artist.