Fediverse/Mastodon meta
We can't even teach instances like picking an email provider because nobody chooses their email provider anymore. They're either in Gmail or they're on a company provided Microsoft Exchange or Google Apps domain.
Teaching federation requires a fundamental social change in the way we treat the internet, a damage caused by the last decade and a half of deep centralization of services. That's not Mastodon or the Fediverse's fault, but it inevitably impacts it.
Fediverse/Mastodon meta
I also argue that, were cloud platforms to be ultimately eliminated from the internet, we would see a resurgence in federation as it would become technically necessary again.
That will likely not happen any time soon, though.