Non-working mothers is a modern anomaly. It used to be a sign of wealth for a man to have a non-working wife. That is why the newly affluent men of the mid-20th century wanted it so much. They came out of the great depression, fought a great war, and wanted a wife at home. You should not judge all of history by this one era.

The work of child care used to fall on the entire extended family. The nuclear family reduced the flexibility in raising children. It was further reduced by a lack of work-life balance for both fathers and mothers. When women started working (again) the lack of flexibility fell on the mothers to fix.

In my own life - I worked, my mother worked, my grandmothers worked, and my great grandmothers worked. I had flexibility through daycare, my awesome husband, my awesome mother, and my awesome employers. I know they are all awesome because when my daughter (a software engineer) faced the same issues, her employer was not at all flexible. She quit work to stay at home with her three boys. I have a bunch of engineering friends who faced the same issues as my daughter. I originally thought they left the workforce out of choice and now I know they did not.