> Because it is useful to have a communication mechanism which is universal. It is a standard and not owned or controlled (censored) by anyone. Sure there a dozens, possibly hundreds, of fragmented chat protocols that can't talk to anything other than their own proprietary clients. But only email is universally available.

I have never found that to actually be useful in practice. Non-universal protocols with proprietary clients have worked well for me - they have been convenient, well-engineered, well-designed, and well-populated by the people I want to talk to.