Wars aren't about just filling up some arbitrary death quotient. If someone is unfit for combat and gets themselves killed unnecessarily they aren't just dying, they're failing whatever task they had, losing potentially vital equipment, and putting the rest of the force in greater danger.

It's not about trading men's lives for women's, it's about not having room to fuck about with underperformers in a group effort. Anywhere the outcome of combat matters, you want men fighting. And anywhere it doesn't matter, then why the fuck are you fighting there?