To be honest, I don’t quite understand why Matrix passes this hurdle and XMPP does not. Matrix is just as little designed for privacy as XMPP. Metadata is also generated, is also not E2EE (as far as I know) and is also distributed further by federation than in XMPP. The quality of the clients is al...
xmpp is closer to IRC than to modern communications protocols. End-to-end encryption, for example, is an optional protocol extension, which hasn't even been formally finalized yet (and probably won't ever be, given it's been 10 years now)