"why/how did it survive?" The earliest blues music survived among folk musicians by them learning it from each other as folk music. There was a popular music industry as of e.g. 1895 and 1905. As of 1905, "Rags" that were rags were being published as sheet music already but "Blues" that were blues were not yet, for instance. Meanwhile, as of 1905, blues music already existed as folk music, as heard e.g. by Elbert Bowman and Emmet Kennedy.