Perhaps it is wrong to make that assumption. There are plenty of people who think otherwise. The point is, grades should not be the main focus of our college experience. We learn nothing from having A's and B's. Our real learning comes from our everyday experiences.
More valuable knowledge comes from learning outside the classroom.
Anyone can memorize countless, meaningless facts and do well on a test. The real challenge is the actual learning of material and keeping that knowledge for the rest of your life. No one becomes a good reporter from a class, they do it in the field. Doctors get their real training in the hospitals. Teachers learn to teach in their own classrooms.