Right now I can sign up at twitter.com and get to see and talk to everyone else who has signed up - where do I sign up for Mastodon and do I get to interact with everyone else who has done the same?
(the fact that this needs to be explained at all should already be a hint that it will never be mainstream)
Ah yes, because users are incapable of learning anything at all
Twitter had plenty of new concepts with replies, quote tweets, hashtags, threads, ratios. The evidence is that people can figure out this amount of new stuff.
"Right now I can sign up at AOL.com and get to email everyone else who has signed up - where do I sign up for social networking and do I get to interact with everyone else who has done the same?"
There's no reason to think people can't come to grips with a federated model just because they're used to a centralized one.
There's no reason the answer needs to be more complicated than Twitter. Options exist, but in the literal ELI5 explanation people can already figure out "how do I message my friend who uses a different phone manufacturer than I do" without a long detailing of the inner workings of signal, or iMessage or whatsapp
That's fine though. Pleroma speaks ActivityPub so you can network with everyone who's using Mastodon, but calling it "Mastodon.tech" is weird.