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

Also: afaik not everything applies to Matrix, e.g. a widely used server logging passwords or a server being able to manipulate chat rooms that extensively