I can imagine the exchange between Stephen King and his agent:
> "Stephen, I'm trying to market your books, but the publishers aren't seeing any engagement on Twitter".
> "Oh I left because I don't want to pay $20 / month to someone I disagree with politically."
> "Have you been hitting the bottle again?"
End of conversation. The value most of these celebrities get vastly exceeds $20 / month. The Twitter-celebrity relationship is symbiotic, nor parasitic.