So women would be freed up to care for elderly relatives or grandchildren allowing their daughters to go to work.
Also because the average age gap for marriage was about five years a couple would retire about the same time. With men's shorter life expectancy, and many jobs done by men having higher risks of occupational disability again the woman would be freed up to care n this case for her partner. There was also the idea that women were weaker and couldn't work for as long, and at that time working women would also be doing pretty much all the domestic chores, cleaning, cooking, laundry, childcare, etc so they were probably knackered.
This is a sociological rather than government rationale