The other night 337K people all registered to vote, simply because Taylor Swift sent one message on instagram.
People come to the platforms FOR the celebrities. And that's just ONE celebrity. The more celebrities on the platform, the more fanbases come with it.
But celebrities are picky. If they think something will hurt their image, they won't do it. Even if theres minimal chance it hurts their image. They have to be protective.
So they need assurance that when they post something, there's zero chance someone else could be posting "as them". Ironically enough, that was the original purpose of twitters blue checkmark.