To work 2 hours per day?

Work 2 hours per day is the title of a small French book published in 1977. What happened/happens to the tremendous productivity gains?


Where is Progress
"I looked at the French economy during two periods of 40 years each: 1896-1936, and 1936-1976. During the first period productivity (i.e. production per head per hour) increased by a factor of 3. During the same period, worktime was divided by a factor of 1.4.
During the second period, productivity augmented even more than in the first: it was multiplied by 3 or 4, but the length of the workday did not significantly change."
The length of the workday has not changed since the 8 hours workday was introduced in...1937, when what became the Fair Labor Standards Act (29 U.S. Code Chapter 8) was enacted but the struggles that produced this law had started much earlier (as described in Wikipedia) and in many companies the 8 hour day has been adopted much earlier, in the early 1900s.
In any case, 76 years later we are still stuck at 8 hours per day... and no paid vacation!