In the late '70s, when 24-track recording was possible but there was no reliable way to automate mixing, mixing records was a live performance, with the producer, the engineer and half the band called in to push faders up and down as the track was bounced to the master tape.
No complicated narratives, no personal themes, no innovations in techniques or cinematography or shots, no daring in the decisions about structure or mixing mediums, and the topics must be serious and yet usually not too divisive in their implications and conclusions.