I'm not well versed in American history. Did anything significant happen then to cause this, or is it just an interesting anomaly?
The part would have been disproportionately true for jobs lower down the socioeconomic ladder because jobs higher on the socioeconomic ladder generally go to people who had more ability to licitly or illicitly avoid selection for military service.
The women's movement also made it "not wierd" to want a job outside the home, and for some a badge of honor. It's hard to articulate exactly what that meant for women, but for my older sister, "not wierd" was being a teacher. For my wife, OTOH, being an attorney was "not wierd", and in fact past the point of being a meaningful badge of honor, it was just a job. We're talking a 10 year time span.
-edit-
And by "just a job" I don't mean to imply that discrimination against women completely disappeared overnight. I remember the day after a re-org, the new incoming manager walked into my neigbor's cube, my neighbor being a rather consistently excellent (female) engineer, and he said, abruptly: "I don't like women engineers.", turned and walked out. Those of us that overheard had a total WTF reaction to that. Luckily those dinosaurs are largely gone from the planet.
https://aneconomicsense.files.wordpress.com/2016/03/labor-fo...
My dad, for example, didn't learn how to type until the late 1990s.