Most people reading what Carl Sagan wrote here will blame our educational system, claiming, not completely without merit, that it stultifies the mind with rote learning required for good test scores, and that it cranks out conformists incapable of critical thinking. Many will go even further, and suggest that this is deliberate, i.e., that government and corporate chieftains specifically do not want people capable of thinking for themselves.
Another huge consideration, however, is that science is not valued in American society. Long before the anti-science people came along, it was obvious to all that our culture approves of wealth, sports prowess, and physical beauty, but has very little admiration for anything else.
Ask one of these high school seniors to name a wealthy person, a baseball player, a musician, and a gorgeous actor. Then ask him to name a living scientist.
The ability to throw a small, hard, leather-coated sphere 60 feet with great velocity and accuracy earns one millions of dollars and the hero-worship of a nation. Discovering a new exoplanet 4 lightyears from here has all the characteristics of Earth and therefore could support intelligent life makes one a nerd.