I've seen many blues shows since the early 80s -- BB King, Albert King, John Lee Hooker, Buddy Guy, Taj Mahal, James Cotton, Otis Rush, Clarence "Gatemouth" Brown....etc.
It's a very rare occasion when I see black folks in attendance.
Well one reason is that the money is in the white clubs. In Chicago when nobody paid anything the blues was performed in the West side and down on 47th street. Then the young whites discovered it through the Butterfield Blues Band, John Mayall and such groups as the Blues Project. This set in motion the establishment of clubs in the safer areas of town such as Lincoln park and the North side in general and the pay drew the players but not the black population as a whole.
This started in the mid sixties when the whites from the U of C community discovered Theresa's.