It wasn't really always the case. If you scroll back, so to speak, a generation or so, the further and further you get, the less necessary it was to win the trifecta of being Attractive, A Dancer, and a Live Performer. Let alone songwriter. There's only so many people that are all 4 and you know all of them by name.
You could be VERY plain looking, and unable to dance at all, and chart in in 1965.
Fred Astaire's original audition allegedly was noted as: "can act, can sing, can dance a little."
Attraction followed from fame, rather than the other way around.
I would argue that it has waxed and waned. 50s most music was written by a composer. Have a songwriter behind a big name like Frank Sinatra. 60s has a surge of bands producing their own music in a smallish crew (Beatles, Beach Boys). But then arena rock was tightly controlled by the industry, but then Nirvana and grunge got big.
That's a really interesting point. Do you think that pattern applies to other genres too?
Yep. And to go to the extreme like Milli Vanilli, when they’re performing they’re not even the one’s actually singing!