I think that we need to talk about the history of software and social software here, because the current status is kind of crazy:

• Most of the big platforms didn’t invent what they are currently doing. Reddit is basically a forum. They had a great innovation with their voting idea, but functionally there is little difference between the many webforums we had before and Reddit
• Twitter is a microblog, which already tells you about its origins. There were blogs before twitter, on their own servers, talking to each other with pingbacks and RSS
• YouTube, well, basically just shows you videos, which of course was done before by people on their own servers

So basically most fediverse is not emulating existing platforms, but trying to go back to an internet we had before the big platforms took everything over. And with ActivityPub we have the protocol to ease some of the pains that the decentralized internet before the web 2.0 era had. F.e. you had to create an account for each individual webforum, which really sucked if you just wanted to ask a question or share something. Reddit with its one login totally took over, because you could participate in many subforums. It was easier to just hop into /r/cooking to ask a question about your lasagna then to find the relevant lasagna forum and register there.