Regarding OP's question, the answer is very simple: sexism. Ukraine is a sexist, backward country unworthy of being considered civilized, and it is showing it once again. There is, obviously, no reason whatsoever to conscript only men and not women; physical differences do not prevent women from fulfilling support roles (even if we consider all women unsuitable for combat roles, which is obviously a stretch), and modern armies have more support roles than combat roles. Israel, which has been drafting women since 1948, has an extremely effective and historically successful army, "despite" women accounting for one-third of its troops. In fact, its army has historically been far more successful than those of the countries of origin of individuals who try to persuade others that women aren't suited for the Army due to biological differences.
Women having to care about children is likewise drivel. Prime conscription age is 18-25, and Western women don’t have children at that age, the age of motherhood in Europe and North America varies between the late 20s and over 30, depending on the country. Women having to give birth to children and their death thus harming the survival of a country is likewise drivel; when a war is over, polygamy is not made legal and surviving men do not suddenly start having children from multiple women. Some women have children with the surviving men, the others remain nubile and childless. Once again, Israel has been drafting both sexes since its birth in 1948, and its more economically and socially thriving, and has been more military successful, than all of the countries where old farts keep repeating the same childish objections against female conscription while trying to sound tough and look like they are presenting “harsh truths”. This is the only “harsh truth”.
Thankfully, more and more countries have addressed this issue in the last few years. Norway and Sweden, two of the few European countries with still active conscription, have extended it to women in 2013 and 2017, and the Netherlands, where conscription exists but is "suspended", changed its law in 2018 so that in case of reactivation of conscription, it will apply to both sexes. The United States are also trying, as they should, to extend selective service obligation to women; this is only opposed by the same relics of the past which recently banned abortion. If there will ever be another draft in this country, it will be for both sexes, and there will be no outcry; on the contrary, there would be an outcry if the draft would be only for men, which is obviously inacceptable. Young men have no interest whatsoever in getting killed for a country that discriminates against them; even in backwards Ukraine thousands and thousands have surrendered, deserted or fled abroad to avoid dying for a misandric regime, the same would happen here on even a greater scale, much to the displeasure of some backwards individuals who posted in this discussion.