In a new paper, Friedman tries to figure out why that increased productivity has not translated into increased leisure time. Perhaps people just never feel materially satisfied, always wanting more money for the next new thing. “This argument is, at best, far from sufficient,” he writes. If that were the case, why did the duration of the workweek decline in the first place?

Another theory Friedman considers is that “in an era of ever fewer settings that provide effective opportunities for personal connections and relationships,” people may place more value on the socializing that happens at work. But the evidence for this “remains uneven at best,” and, once again, “its bearing on the abrupt change in trend in the U.S. workweek in the 1970s is far from established.”

A third possibility proves more convincing: American inequality means that the gains of increasing productivity are not widely shared. In other words, most Americans are too poor to work less. Unlike the other two explanations Friedman considers, this one fits chronologically: Inequality declined in America during the post-war period (along with the duration of the workweek), but since the early 1970s it’s risen dramatically.

Keynes’s prediction rests on the idea that “standard of life” would continue rising for everyone. But Friedman says that’s not what has happened: Although Keynes’s eight-fold figure holds up for the economy in aggregate, it’s not at all the case for the median American worker. For them, output by 2029 is likely to be around 3.5 times what it was when Keynes was writing—a bit below his four- to-eight-fold predicted range.

This can be seen in the median worker’s income over this time period, complete with a shift in 1973 that fits in precisely with when the workweek stopped shrinking. According to Friedman, “Between 1947 and 1973 the average hourly wage for nonsupervisory workers in private industries other than agriculture (restated in 2013 dollars) nearly doubled, from $12.27 to $21.23—an average growth rate of 2.1 percent per annum. But by 2013 the average hourly wage was only $20.13—a 5 percent fall from the 1973 level.” For most people, then, the magic of increasing productivity stopped working around 1973, and they had to keep working just as much in order to maintain their standard of living.

What Keynes foretold was a very optimistic version of what economists call technological unemployment—the idea that less labor will be necessary because machines can do so much. In Keynes’s vision, the resulting unemployment would be distributed more or less evenly across society in the form of increased leisure.

Friedman says that reality comports more with a darker version of technological unemployment: It’s not unemployment per se, but a soft labor market in which millions of people are “desperately seeking whatever low-wage work [they] can get.” This is corroborated by a recent poll by Marketplace that found that for half of hourly workers, their top concern isn’t that they work too much but that they work too little—not, presumably, because they like their jobs so much, but because they need the money.