It must be horrid to be middle-aged and still famous for something you did when you were a gobby kid. You'd feel trapped, like you couldn't move on. It would be like carrying a corpse around.
And maybe that's the reason- aside from the money, aside from wanting to prolong his fame- why Johnny Rotten did that stupid butter ad. He wanted to ditch the cadaver.
He wanted to upset his fans.
And yes, it's always sad when a hero sells out.
Simple remedy: don't have any heroes in the first place.