Johnny Cash's concert was in the late 60s, before the string of prison riots in the 70s which left several correction officers dead and the rest of the industry

Johnny Cash's concert was in the late 60s, before the string of prison riots in the 70s which left several correction officers dead and the rest of the industry hyper-defensive (all of the riots, except one involving Cuban exiles who were going to be deported, were due to prison conditions AFAIK). By this point, the war on drugs was in full swing and the prisons were filling up as fast as humanly possible.