Last I looked XeSS was still closed source (no matter what Intel says about it) so saying 'XBox supports it' is akin to saying XBox supports DLSS. Unless the vendor decides to port it - it doesn't, and developers aren't the ones to point fingers at here as there's f-all they can do.Xbox also supports Xess that is in the market for ~4 years but no game on it is using it.
What AMD is doing is a whole different story obviously - but that one (assuming hw isn't limiting in ways people don't understand - which could still be the case) I'd put more on MS not giving a damn about XSX (definitely not devs either). As I doubt AMD would stop them if they actually you know - tried.