Looks like it’s for feeds and the fediverse
Well, for one, like the guy says below, it was often said to people as a means to explain how federation works, which immediately failed by way of people not thinking about or knowing how email works, either.
For another, my emails look like emails everywhere, both on source and destination. I don’t have a different character limit or feature set about what I can slap into my emails depending on what client I’m using, and I’m reasonably sure my email looks the same on the other end, no mater what client the recipient is using.
So the back end may work like email (not really, but it may approximate it), but the front end sure as hell doesn’t, so the explanation is more confusing than anything else.
Also, not the part of Mastodon specifically that people didn’t understand, they just tried to log in, were presented with a thousand instances, told choosing which one to use was super important but also that it didn’t matter and they should keep changing instances later, but also that migrating instances was not an easy process, but don’t worry, it’s just like email.
It was a hilarious endless loop of a conversation, like a Monty Python sketch. Or seeing people try to tell normies to use Linux.