Gmail isn't a protocol, nor is it open. People don't self host email because 1) the protocol doesn't make it easy to deal with incoming spam on a small scale,

Gmail isn't a protocol, nor is it open. People don't self host email because 1) the protocol doesn't make it easy to deal with incoming spam on a small scale, and 2) giants like gmail tend to automatically flag unique email domains as suspicious. Which is a valid criticism of the federated model, or rather the people using it. If more people found value in decentralization, in theory they would also be more critical of their node management, opting to reject anti-competitive behavior in a democratic way. Unfortunately, for democracy to work, citizens have to be educated and fight for it. If they don't, it's easy to have centralized, ostensibly totalitarian walled gardens. We just need to make sure fediverse accounts are easily transferable between nodes in a standardized way, something I don't think mastodon does well, and email doesn't do at all.