This gonna be long, might just want to ignore :)

It's not that easy or we'd be doing it already.

Problem one: Techie. The term ‘federation’ may evoke images of a space opera for some, potentially alienating a large audience who may perceive it as overly technical or complex. This is despite the numerous companies utilizing federation to effect positive change in the world. The reality is, the average person may not immediately associate the term with these beneficial applications.

Problem two: Bifurcation. Any explanation and advantages you give for decentralization will feel inadequate compared to their worry and confusion over bifurcated communities and the next several problems in this list.

Problem three: Four letter word. Users on centralized platforms often view ‘Federation’ with skepticism, insisting that it’s too complicated. "Eww you don't want to go over there, that place is just a hot mess, it's too complicated. Just stay here, it'll get better here."

Problem four: Identity. Everyone on centralized social is completely wrapped around their identity. I am MrMcSniggles, it is my legacy and there can be only one. In Federation, there can be a thousand MrMcSniggles. Verification and ID ownership is pretty weak in the Lemmyverse.

Problem five: Login. Oh what server do I choose? We tell them that it doesn't matter, but if they pick an extremist node, or a node small enough not to get global community traffic, they're going to have a bad experience. They're all going to gravitate toward the largest nodes, which is better these days but goes against the whole point of federation.

Problem six: Discovery. So who will see posts? That's simple, yet mind bending for the uninitiated. You post it on your local node. If no one on your local node shares or boosts it, the global community will never see it. What posts do I see? Well you see, at best, what the people on your instance are seeing. Oh so that's everything on the federation? No. Oh so what do they see. That discussion is also off putting enough to turn many away.

Problem seven: Permanence and Migration. If you get through login and they're still onboard, what happens if a server goes tits up? Do my old posts still stick around? Well, kinda, but not really. Do I get to keep my old subscriptions at least? (hopefully soon) For the moment, no, unless you sign up for this third party service.

Problem eight: Algorithm. You go to the community tab, you select all, let's see some raw unfiltered.... OK, look at that, bots reposting everything on Reddit. Bots reposting every game for every team for every sport. What do I do? Well get to blocking. Oh I can block that easily? Well, it's like 4 clicks per block, if it's stuff you know you don't want you might be able to block a user and get multiples done, sometimes it's just a community you want gone, and another, and another and well hell, this is another full time job. They're going to miss the Algorithm. Trying to convince them that less doom scrolling is good is often a fools errand.

Problem nine: Defederation. Every time a node gets defederated, there's a huge stink. We do it really often because we lack admin tools to handle global individual/community censorship. In one paragraph we tout free speech, but in the same paragraph we end up talking about the banhammer required to keep the communities civil.

Solution one: You can explain that federation is like email providers, which is closely resembles, but the finer points on the analogy are lost on the uninitiated, it turns to confusion, begs more explanation, ends up making it sound more complicated than it is.

Solution two:
You can say that Federation is a backend thing and it doesn't affect your social media except that you have to include what service you're using in your @'s This works pretty well, but it breaks your request to tell them why federation is so good.

Solution three: You can dumb it down and make a series of points ignoring the negatives. No one can take down the network. You are not a product to be sold, you are free to move around the network as you see fit to find your home. As other services video, images, audio, blogging pop up, you can interact with them from your existing accounts. But all these end up being far more complicated as they start asking questions.

None of these are great, upside and downsides. I really wish we could come up with some kind of nickname solution like IRC, that and some good admin tools would go a long way toward reducing the excuses people use to stay away.