Perhaps selling out for some bands is continuing to do the same music they've been doing for three albums now even though their artistic soul wants to go a new direction. But if they do go a new direction... sad irony, eh? You never know what's going through their heads.
I loved when Metallica came back after five years, everyone with short haircuts. People took one look at them and cried, "Sell-outs" like they all woke up one day and said, "Hey! Let's all go cut our hair!" The eighties were over! You hadn't seen them in five years! Granted, their album was received even less warmly.
"He lived hard and died stupid."