One possibility is that touring musicians lose touch with ordinary life, and therefore no longer create anything that people can relate to.
Nick Cave is a counter-example to the above, btw. I think he's just gotten better and better with age
Nick Cave is a counter-example to the above, btw. I think he's just gotten better and better with age
Reminds me of an article I read about R.E.M. around the turn of the millennium. The journalist notes that the band members (now all multi-millionaires) now spent their time moving from one posh luxury hotel or perfectly air-conditioned space to another around the world, living in an international cosmopolitan bubble even when not touring. This seemed the very antithesis of the struggle and feeling of local community from which several great rock subgenres had emerged, and it was no surprise that R.E.M.'s work had become bland.
In another part of the interview, Andre Benjamin said he loved going to the laundromat, and his biggest musical aspiration (at the time of the interview) was to play the bass clarinet well enough to be able to play along with anything/anyone at the park or beach (condensing/paraphrasing).
I think it's a combination of things, the career of a pop musician appears to be terrible for their art - probably bad for most of them as people, too.