It’s not saying “gender dysphoria is not a diagnosis that exists anywhere” it’s saying “believing yourself to be transgender is a substantial enough mental illness and flaw in character so as to preclude military service.”

This claims that having gender dysphoria is some sort of deficiency, and not just a non-standard identifier. This invalidates the identity of trans people, and calls into question their legitimacy.

Of course not, that would provide legitimate status, and would allow them to leave their husbands. Best to connect their presence here to the man so that their leaving is under threat of deportation.