Email was invented in 1983.

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 stunning ecosystem of near inatant 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 with easy, no or low effort walled gardens.

Federation was and is a reasonable way to host things, but comparing it 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 servers. Hell, AOL tried to choke the internet itself, including email, to death and almost succeeded in the early 90s because it was an “all in one” solution. They had aol only webpages and everything.