[bzbarsky]

Why unexpected? The Soviet Union did too. A few reasons for that (for the Soviet Union; I know less about China):

1) One of the premises of communism is equality of all people, including equality of men and women. As a result, a bunch of official barriers to women's labor force participation that existed in the US up until recently were removed quite a bit earlier in communist countries. Not only that, but the right to a job was considered a basic human right in the Soviet constitution, and not having a job was a crime punishable by jail time starting in the early 60s (see https://en.wikipedia.org/wiki/Parasitism_(social_offense)#So... for some basic details). Note that this did not necessarily affect societal attitudes about household labor, by the way: women were just expected to both work _and_ do the cleaning/washing/cooking at home...

2) Female employment in the US surged during WWII to make up for all the men drafted into the military, then dropped as the size of the military was reduced in the aftermath. Something similar happened in the Soviet Union with women stepping into "men's jobs", but without as much of a corresponding drop after the war. Something to do with the fact that US deaths in WWII (combat and non-combat) were ~400k, which was about .6% of the male population in 1941, on the assumption that most of those deaths were males and males were half the total population. For the Soviet Union estimates for military deaths (mostly male) in WWII vary from ~8 million to ~14 million (see https://en.wikipedia.org/wiki/World_War_II_casualties_of_the... ), which corresponds to 4-7% of the 1941 total population. 8-14% of the male population if the pre-war breakdown between male and female was 50-50, which may or may not have been the case. Plus whatever the breakdown was among the ~10-15 million nonmilitary deaths in WWII in the USSR... But the upshot was that there were a lot more women alive than men after the war, which reduced he "men coming home and taking back their jobs" effect, because the men just did not come home.