Four years makes sense for students who are trying to get a liberal education and therefore need to take a few dozen courses in philosophy, religion, classical and modern literature, the fine arts, classical and modern history (including the history of science), plus acquire fluency in a foreign language and take basic survey courses in the social sciences. The percentage of college students who want to do that is what? Ten percent? Probably that is too optimistic. Whatever the exact figure, it is a tiny minority.
For everyone else, four years is ridiculous.
Read the rest of Charles Murray's essay "Down with the Four-Year College Degree!"