The textbook explanation for why Keynes' workweek prediction failed is that he failed to account for the shift to a service economy, which provides ample room for people to expand what they work on and what they spend on.

The crisis within that explanation is that the number of people employed in the "service" category has not grown proportionately with gains in productivity. In fact, it's barely grown at all. The type of job that has filled the gap is "administrative/clerical."

This observation has led David Graeber to propose that perhaps Keynes was essentially right, and that the only reason we don't have the shorter work week is basically that we refuse to let it happen. We would rather continue "working" whatever number of hours was customary in our culture (40 hours a week in the US, less in Europe, many more in Asia) and if there's not enough to actually do (there isn't) we have a small number of people do the work for 40 hours and the rest are just managers and administrators sitting around in a redundant meeting or staring at a screen waiting for the next redundant meeting.