And yet incomes have held stagnant through the entire rise of college attainment. That contradicts the notion that there is more money to be made.

Within a given population, those who are born more capable will earn more than those who are less capable. Those who are born more capable are able to go further in school and be more productive in the workplace for the same reasons. Someone born with a crippling disability that forced them to drop out of high school also struggles to find gainful employment for the same reasons.

However, over time, those in similar standing seem to end up making the same amount of money no matter what. If the existence of college and everything associated with it were to magically vanish, those born more capable would still earn more money over their lifetime than those born less capable.