80 years ago women could afford to stay at home.
But last year, 2 of my friends fire their 5 employees and started again, them alone. They made the calculation: there productivity ratio was better with only them 2, than with the 5 part time workers they had that they were paying full time + benefits. And their team was "good" in my book. Most teams I meet are not, and I travel from companies to companies all the time.
If this were really the problem, it would be pretty easy to solve... (HINT: this isn't really the problem!)
These factors are irrelevant when compared with the fact that the active population essentially doubled since WW2 with women entering the workforce.