The whole concept of selling out is both particular to a person or in group and also cultural. A related concept is ‘poser’ or ‘poseur’. I think it’s more about fans thinking they’re losing their importance vis a vis the performer or artist. The artist is no longer “exclusive” to them, so to speak as well as no longer an idealized representation of them, the fans.
Was it his choice? I swear one of the introductions in The Complete Peanuts talks about how Charles Schulz spent much of his life trying to buy back the copyright to his strip.
(Which let them do things like "buy Heavy Metal and run it at a loss for a while" and "start a publishing company that became infamous for handing out huge advances to their comics buddies that let them spend a couple years on passion projects instead of turning the Superhero Crank for Marvel/DC", both of which I feel are perfectly delightful ways to deal with making the kind of money they made off the Turtles. The history of Tundra Press is a hell of a ride, if you can find it.)
https://lareviewofbooks.org/article/selling-newspaper-comic-...
Unlike what happened with Dr. Seuss. Of course, no one can totally control what happens with his or her creations after he or she passes away. Look at how the vultures descended the moment Christopher Tolkien passed away.