Gurl, selling out and being mainstream is two different things but ok.
Pop artist can't sell out because they have been pop.
Leaving your artistic integrity and changing your sound to be more commercial to appeal to a mass audience THAT IS selling out. There's a difference between having a hit song with YOUR sound and having hit song because you changed your sound. Boo boo kitty.
Ellie, Maroon 5 and more recently Taylor (to an extent because she's always been somewhat pop)
Ok, I IS done.