Because so many civilians died, including women, and harsh living conditions due to wide spread destruction.

I am not even in Russia, but that war pulled so much out of every region, including mine (which did not see fighting directly, but provided many conscripts and resources), that after the war there simply wasn't much to eat or too many people to work the fields. My grandparents first ate caramel candy in 1952, IIRC. Good luck increasing your fertility rates in these conditions.

The URSS did draft women. Also, massive civilian casualties.