I read on https://www.aei.org/publication/leisure-college-usa/ :

Study time for full-time students at four-year colleges in the United States fell from twenty-four hours per week in 1961 to fourteen hours per week in 2003.

The authors give some inconclusive statement regarding the reasons behind the trend:

The decline is not explained by changes over time in student work status, parental education, major choice, or the type of institution students attended.

Evidence that declines in study time result from improvements in education technology is slim. A more plausible explanation is that achievement standards have fallen.

I wonder why the time spent studying has declined so sharply in the United States over the the past few decades. I am only looking for data-supported answers (or pointers to them).