Yeah there are large threads on them but because the API has been developed for WiFi, moving to a mesh like ZigBee would be a substantial rewrite although matter would be a lot easier than ZigBee, which got written off a long time ago as just too large if I remember right.

It is also a huge project for people to start developing on, their core team isn't massive, so there is a large barrier to entry for such a thing. It might be happening in the background though, no idea.