The point is - research. Teachers, Professors, and Instructors, usually want the student to put forth the effort to actually grab many sources for the paper, when usually the author of said paper will simply grab the wiki article for the main source of info and tack on other sources to say "Hey teach, I got the required amount."
A good teacher would fail them on the spot, but many times I've seen half-ass papers score near perfect scores. Depressing, but there is a huge lack of quality of work for the so called college paper.