Part of the problem may stem from habits kids acquire in high school, often with parental blessing.
Say the state grants lottery scholarships to students with B averages and above. The student learns he is in danger of making a C. Mommy and Daddy go to the principal and get him shifted to a less rigorous class, or even worse, arrange for him to drop entirely (one math class I know about ended the year with three students. At a public school).
Once in college, the kid signs up for 16-18 hours, drops the class where the professor expects too much, or isn't easy to understand, or "gives him a hard time." To re-take the class, he may have to wait for another year since certain required classes are only offered in the fall (or spring) but not in the summer.
It's a vicious cycle. First, the student eventually realizes the class he dropped was a prerequisite for another one he must take to graduate with his buddies. He might try to get the school to let him take both courses simultaneously. If he does so, the workload adds further challenges. If the school is decent, they'll tell him to forget it.
Second, universities have a scale for how much they refund on dropped classes. By the time the student makes such a move the investment in time cannot be recovered -- and he might only get a fraction of his tuition back. So he's stuck with paying back a loan for a class he stopped attending after week three.
Parents can set clear expectations for four-year graduations, penalties for dropped classes, and demand regular feedback on class performance. But if they've been allowing Junior to dodge the bullet all along, they've already set the example.