It was revolutionary, the utter example of a "killer app" that had people and businesses running out to buy computers just to replace paper memos. You setup your mail server to hook into that brand new, stunning ecosystem of near instant communication from across the world.

Now there are 6,000,000,000 "killer" apps you can install in seconds from your pocket computer. I can hit "install" and be talking face to face with a stranger in Singapore in 30 seconds, all from easy, low effort walled gardens.

Federation was and is a reasonable way to host things, but comparing current systems to email is a misnomer. People dealt with federation because they had to. If gmail has existed in 1983, no one would have had their own federated email servers. Hell, AOL tried to choke the internet itself to death and almost succeeded in the early 90s because it was an "all in one" solution. They had aol only webpages and everything, including email. Its a twist of fate that they failed, mainly due to the onset of always on broadband, not because people didn't want things easy.

Make things easy, people will use it. They will only do hard if they have to.