I think the point is that it builds on existing infrastructure that almost everyone already has in their life. Whether you self-host, use a niche provider, or a mainstream provider, email provides a pretty interoperable starting point which isn't a walled garden and doesn't have to be owned by FAANG.

Are there some compromises? Of course. But creating new accounts, or using new services isn't one of them. Email-speed instant messaging is good enough for me.

And to be honest, as much as I like Matrix, it has plenty of compromise of its own - including speed/reliability when using their own servers.