I think what people take for granted is this was true even before digital piracy. Most exposure to music was through radio play, and cassette copying was fairly popular from 80s onward. Rock wasn't dead yet (or at any rate, it was far more alive) and concert-going was (I think?) bigger among youth in general. Owning records was always an expensive thing and the majority of music fans didn't try to go broke buying every little thing they enjoyed.

Which brings to mind, I always wonder how pop artists are reaching platinum sales today, because their physical media has zero prestige to most collectors. Is it from radio stations and DJs or something? The figures just don't make sense to me. Pop music fans use Spotify or the radio, by and large.