Why don't more people use XMPP?

Duplicate of: Why not XMPP? TL;DR it’s not as secure or private. Also not as feature rich (or popular?) as Matrix which is overall a slightly better federated platform. SimpleX Chat is a much better alternative if you want an anonymous (be sure to use Tor!) and decentralized messenger. Cwtch and Briar are also potential alternatives depending on your criteria.