But why does that line of reasoning not apply to rich YouTubers and Twitch streamers?

If influencers stopped working, their revenue would go down drastically, which can't be said of Rowling. So in a sense they have to work for a living, but they're also so rich that they could stop working if they wanted to. It just seems like they're similar situations.

If you can call an athlete or a movie star labour aristocrats, it seems like that label would also apply to successful authors and influencers. They're all propped up by the industries built around them.