In particular you mean XMPP with federation between servers. In general capitalism is a force against interoperability. SMTP is an open standard. No one is mak

In particular you mean XMPP with federation between servers. In general capitalism is a force against interoperability. SMTP is an open standard. No one is making any money on email clients. The good ones have become such a commodity that they are open source. When people go looking for email hosting they get to choose between more or less identical services. SMTP is simply a terrible market. When everyone starts encrypting their emails then Gmail will cease to exist.