Which server do you want to use is like asking "Do you want Gmail, Outlook or Yahoo for email?" it really isn't that big of a deal, but maybe people these days have a hard time doing that too...
...it would be if in your analogy GMail blocks Yahoo because they don't like the politics of their CEO, Outlook blocks both GMail and Yahoo to create a safe space, and you left Protonmail out of the list entirely because almost everyone else is blocking them for not banning users who email the wrong kind of porn to each other.
It's not a big deal until you realize the notion that they all talk to each other is mostly a lie and all the big ones block dozens of instances each. Hell, the threads on the larger instances about whether or not Threads and Truth Social should be defederated if they ever enable federation were some of the highest activity topics on Lemmy for a bit. So was people cheering about Burggit shutting down their lemmy server.
People always use the email comparison but it's really not the same, it's more complicated than that. We know it's not too much of a big deal but it is when you don't know what it means to be on a server.
I remember being presented with a choice of servers myself and wondering what on earth it meant, and just wanting to join the "default" one. Ultimately it doesn't matter too much but at the time it feels like a big hurdle.