It's only a fluke because we've allowed the resources that once enabled this period to accumulate at the top so that it's not feasible on a broad scale any more.
The only reasonable explanation I can see is a distribution-of-wealth lens. Workers clearly had much more bargaining power during that era, but why? Is it because so many men were killed during the war? Because women who had been working in factories were expected to become stay-at-home mothers? Because of insufficient automation?
Yet Indian middle class was still very distinctly one-income driven.