> If university stopped providing an earnings boost from attending, 90% of students would quit tomorrow.

Maybe 10–20% would quit for that reason. There would be more attrition if you could get common jobs (such as teacher or nurse) that currently require a degree but don't pay that well without formal education.

Most people don't care that much about money. Sure they would like to have more money, but it's not the primary factor that drives their major life decisions. People are generally more interested in stable careers that pay their bills and seem like something they could continue doing until retirement.