The only way to get on Xbox is via Marketplace. Fenix said part of their simulation code is running outside the sim which is impossible on Marketplace and therefore Xbox.
In case of FBW the issue is on the one side the GPL license which is not allowed in the marketplace and on the other side it’s also about resources being able to provide support and testing for this platform.
So for the Xbox users I cross my fingers that the upcoming Aerosoft Airbus products will find their way on XBox (I’m sure they will).