Bob Dubery wrote
. For him, Sgt. Pepper’s was a turning point: Afterward, musicians began thinking of themselves as artists rather than as entertainers. When the Beatles became “purely a recording group,” he writes, “they pointed toward a future in which there need be no unifying styles . . . bands can play what they like . . . and we can choose what to listen to in the privacy of our clubs, our homes, or, finally, our heads. Whether that was liberating or limiting is a matter of opinion and perception, but the whole idea of popular music had changed.”
Well The Beatles had already embraced the studio as an instrument when they recorded
Revolver There were several cuts on that album that they couldn't have done live - and probably had no intention of doing live.
I do think there was a certain change going on at the time. The Beatles were in the vanguard, but were not the only "pop" artists who were getting ambitious ideas. I think that there were "pop" stars who wanted to be taken a little more seriously. Lennon & McCartney amongst them, but also Brian Wilson of the Beach Boys. Plus Phil Spector had already unleashed several singles that could not be reproduced live - they sounded fantastic on radio or on record players. Leonard Cohen released his first album in 1967 - but declined to tour.
So the model had been changing - with the "record", played on TV or radio and then in your living room, rather than the live performance being the actual product.
Things were getting more serious. I think the prime mover there was Dylan. I can see how Lennon or Wilson would want people to
listen to them in the way that they did to Dylan. The Beatles famously (or infamously) played loads of shows where they could hardly hear themselves above the audience and so they were pretty sure the audience couldn't hear anything coming off the stage. They could play great and nobody would notice. They could play crap and nobody would notice. The girls went along to scream and swoon, and the boys went along because the girls went along.
Maybe the audiences killed rock 'n roll?