Yep. One man can impregnate multiple women, but each woman can only bear (usually) one live young at a time, so a loss of breeding males is far less significant than a loss of breeding females.
Plus male average strength is much higher than female, so most men can be made into effective enough soldiers, capable of carrying the heavy equipment, body armour, weaponry etc fairly quickly and easily. Most women will require a far longer time period to develop the physical strength required, and a far greater number will not be able to do so.
Plus standard issue military gear is made for men not women, so body armour etc won't fit women. Interchangeable kit on a battlefield is useful.
Plus men have higher levels of aggression, due to testosterone and societal conditioning, making men more easily shaped into soldiers who will kill when ordered.
Plus the psychological impact of being able to tell men they are fighting to keep "their" women safe.
Plus women are vulnerable to rape in war. Women being raped has a detrimental impact on the moral of the country/ fighting alliance - babies born of rapes by enemy soldiers disrupt the "us Vs them" dynamic.
Really, there are a lot of reasons why women haven't been subject to the draft, none of which apply to transwomen.