Because let’s say you’re Tom Hanks. And you get TomHanks@Lemmy.World
Well, what’s stopping someone else from adopting TomHanks@Lemm.ee?
And some platforms minimize the text size of platform, or hide it entirely. So you just might see TomHanks, and think it’s him. But it’s actually a 7 year old Chinese boy with a broken leg in Arizona.
Because anyone can grab the same name, on a different platform.
If “TomHanks” is his username on every other service, like twitter, and youtube, and tiktok, and instagram, then he would want to use it when he comes to the fediverse. Now, if only ONE person can have the username TomHanks (and it just so happens to be @Lemmy.World), then he could send a cease and disist letter, and if that doesn’t work, a lawsuit. Madonna did it in the 90s with Madonna.com.
However, if TomHanks@Lemmy.World can exist, and TomHanks@Lemm.ee can exist, and TomHanks@piefed.social can exist and…and…and…then it gets a little impossible for him to really own that username, because it can be duplicated on an infinate amount of instances, some that may not even exist when he shows up to the fediverse.
But if only one instance can have TomHanks, than he could absolutely show courts he’s had a vested interest and usership of that identity and thus that’s HIS username. Even on services he’s never signed up for. Like if he doesn’t have an instagram account at all, but someone else starts using TomHanks on instagram, he can take it to the courts that they are not allowed to do that, because that’s his username.
But the way the fediverse is currently set up right now, that’s not feasible. Because he could enter a court battle with TomHanks@Lemm.ee, and then 5 more instances with his username popup. And eventually it becomes harder and harder to prove that people know his ownership of that username if there’s 500 other people also using the same username. It’s the reason you can’t email celebrities. They can’t control their presence in email, so they don’t use that as their identity.