This is it. As a country sending your women to fight is a very bad longterm-strategy. Imagine WW1 fougth with mostly women in the armies. In OTL it virtually wiped out a male generation in France. If that would happen to a female generation, that is a major screw up for the country. Birthrates would plummet.While certain roles could very easily be female majority, there is a long standing biological reason why the female majority military has not ever occurred except in rare instances. It really does not have to do with strength/muscle mass per se. Women get pregnant, women lactate - so in order to reproduce women would need to be out of active use for at least part of a pregnancy, and even with wet nurses before formula and refrigeration if you don't breast feed babies starve. Humans usually have one child at a time and more than one pregnancy every 12 months is not the norm - breast feeding does reduce fertility but is not perfect birth control, but it does reduce fertility. You can lose a high percentage of the males, but if you have enough fertile females your society survives - NOT the other way around. Don't forget that in the "good old days" infant and maternal mortality was an issue.
If pregnancy is shorter than 9 months, if multiple births are the norm, and other biological changes happen then the need to "preserve" females for continuation of the tribe/society is reduced. If some time in the future we have "artificial wombs" so embryos are created in the test tube (if you will) and transferred to such a device until birth, combined with the preservation of sperm and eggs (which we already have) then the biological reasons go away and society can rewire itself.
On the plusside: those kind of losses would bring the leaders much sooner to negotiations for peace, because they would knew it would take decades to recover.