Mostly, the role of the school is to provide workers to the economy, and high ability is not enough in the marketplace. Volume of work produced is usually even more important. Hence, a school system that places heavy time demands on students is well-calibrated to produce the workers employers demand. This is true in both private and public sectors. A tweak that allows high grades with low output is likely to lead to a subset of workers with high ability and a lousy work ethic, who would largely be unemployable.
Furthermore, the growth of two-earner families has frequently left children shortchanged for parental attention, who would traditionally be the source for learning essential life skills like time management and priority organization. Society has taken notice, and when it comes to interventions, the biggest bang for our buck is to transfer more responsibility to the schools.
