The enemy doesn't just get to pick and choose which units that they can direct "all" their fire power on based on the demographics of a unit, war doesn't work that way, and what general would not want all male military units?
America can lose wars, and can cease to exist as a nation.
Females mean lost battles, which can lead to lost wars. In a major war, to a nation powerful enough to force our complete capitulation, then that means we become theirs.
Exactly, which is why there wouldn’t be any all-female units.