Matrix has introduced some really neat innovations compared to XMPP:
- decentralized conversations instead of centralized ones
- MEGOLM
- Cross Signing
- monolithic protocol (i.e. one true way of doing things officially)
- easy sync of (encrypted) history between sessions
These are reasons why people use Matrix and not because of misinformation about how private it is
Going to keep using the IETF XMPP Standard then.