[I]nstead of accelerating growth, what we got from this increase in labor supply was a loss of earning power by working class men.
Arnold Kling goes into more detail:
To me, the explanation for the data in Alex's post is that the job structure has changed to diminish the relative importance of physical strength. This brought more women into the labor force, and it reduced wages and employment prospects for a significant proportion of the male population. This changed marriage, as Wolfers and Stevenson have pointed out, from something based on production complementarity (women do housework, men do factory or farm work) to consumption complementarity. This results in more assortive mating by income, creating lots of household inequality.