Mostly because millennial dads wish their fathers spent more time with them

I would agree- there are some serious flaws with the proposition. 1943 was in the middle of a world war for one thing. Men were being drafted and if you had a child born in 1941-45, you might not have seen them much of at all until they were out of diapers. But beyond that- the social norms for the time were different. As you say- when you look at the percentage of women who had jobs pre war- maybe 28% of women worked while 96% of men over the age of 10 participated in labor. During the Great Depression- there was additional bias against hiring women with the logic being there weren’t enough jobs- so having both heads of a home work while another home had no “bread winner” was unfair. Of course women weren’t excluded at random- sexism and gender bias played roles in choosing which head of house would be the one to work.

But through much of the early 20th century and even to a degree in the 19th century- a middle or upper class woman working was seen as sign of poor social status. That a man or family couldn’t provide- and it was far more common for lower income and minority families to have working moms than it was dominant majorities and middle/upper class families.

It then of course made logical sense that if one partner’s job was to enter the outside workforce and earn money, the other partner would tend to the home and child care duties. As you say though- seeing the trend change because women now have a choice is a good thing. In an economic climate where dual income homes are often a requirement of survival or a major lifestyle boost- seeing parents share economic and home duties shows a much more comprehensive and fair division of labor. But whatever works for people- there’s nothing wrong with “stay at home” men or women so long as there was choice and agreement and it works best for all involved.