I keep hearing "mastodon isn't good for [type of celebrity], they have to go to [other platform] for engagement"

It's not the celebrity type [scicom personality, journalist, author] it's the attempt to run a celebrity account at all that doesn't work on the fedi.

There are heaps of well known people on the fedi. Either it's not obvious that's their day job or they're just quietly being that in among posts about walking their dog. Coming to the fedi trying to sell your day job and hoping people will 'engage' is odd. Like going to the playground or the museum and being mad that bystanders didn't engage your about your day job despite the sandwich board you're wearing and your refusal to talk about any other topic.

Going into a social environment broadcasting [📢this is my content, engage with it📢] is an obvious recipe for disappointment. No one cares about the things you're broadcasting. Show us your dog. Did they have a nice walk?