Pop = popular = commercial. As we get older, it just becomes more unknowable, more unlistenable, more alien.
Talking of alien, my (bemused/wtf) reaction these days to catching thirty seconds of Nicki Minaj is surely the same as my parents' reaction to the first pop songs I remember loving on TOTP (Baggy Trousers, Stand and Deliver, etc), isn't it? As it should be.
(Don't open the link unless you want to fall down a rabbit hole to another dimension, obvs.)
Eisler was John Lennon forty years early.