Some would simply call it an evolution of style, and others might call it a sellout. I’d like to hear your examples of musical acts that changed so radically over time that you’d consider it a sellout.
My example would be Jefferson Starship. Their first album was “Blows Against The Empire”, which was about hippies hijacking a starship. https://www.youtube.com/watch?v=HzclibWeXM8&t=1126s
Grace Slick was the first person to say “motherfucker” on television when performing their material.
They went from that to shedding personnel, renaming themselves “Starship”, and making pop music. https://www.youtube.com/watch?v=IDI2WQJyE7I
What are your before and after examples that you consider a sellout?
I’m not sure this is exactly what you’re looking for, but it literally a “sell-out” and has always bothered me. Jim Morrison never wanted his music used for any other purpose, but the rest of the band went behind his back and sold a song (I think to Ford) for advertising.
Then there’s Bob Dylan. Never literally promised not to do advertising, but “Song To Woody,” on his very first album comes about as close to a promise as you can get. And then selling his entire song catalog? Come on!
I think selling his catalog is a smart move. It cements his financial stability for the rest of his life, and probably his children as well. But yes, once he’s sold it, they can do whatever they want with it.