You think the white musicians picked up the songs from having the black artists play it to them? Nonsense. They stole them from the recordings by the independent labels.
And, although early blues was an oral tradition amongst black musicians in the USA, there were many recorded albums (with discreet songs under copyright) by black blues artists which didn't achieve commercial success for largely racial reasons. The white artists (and labels) then cynically took whatever they wanted from these records, recorded the songs themselves and made a fortune through 'sanitising' the blues for a white audience. Only much later did some royalties and credit go to the original songwriters through lawsuits and out-of-court settlements.
