we have experience with XMPP, and it doesn't provide metadata privacy, and the security of e2e encryption has many limitations. So we're building something better.
The core problem of XMPP is that it was protocol-first, and it's a dead end for any widely adopted software system - it has to be product-first.
We only have wide adoption of the Web thanks to Netscape who made it a product people can use, disregarding competing browsers.