Answer:
the standard of living increased
Step-by-step explanation:
Between the years 1948 and 1990, the level of productivity in the United States of America increased tremendously, to the extent that it was in the doubled fold. Consequently, this increase in the level of productivity simply exemplified that, there is a substantial increase in the standard of living for the average American.
Hence, it can be concluded that, in this case, the workweek didn't get shorter because "the standard of living increased."