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 also very differing.
I also see the advantages of Matrix and use it myself, but I find it quite interesting how an extra category was recently created to keep Matrix in the recommendations, although it does not support PFS, while XMPP was removed for reasons that also apply to Matrix to a large extent.