*lack of public exporters. Because of the NDAs around shipping for these platforms, no one can "advertise" that they have the exporters, but the truth is that there are consultants/gamedev shops who have done this work for all of the current platforms. You just have to get in touch with them via the community.
EDIT: This page has some backstory: https://docs.godotengine.org/en/3.0/tutorials/platform/conso...