Ivory Tower for Free

I really don't understand why prestigious private universities put up some of their courses and lectures on-line for free. Sure, education is a public good and so on. But isn't it the point of elitist universities to be elitist and restrict access to their resources? At any rate, some of the world's leading universities have free content on-line for us all to enjoy. Here it is:

Columbia University

Harvard University

M.I.T.

Princeton University

Stanford University

University of California, Berkeley

University of California, Irvine

Yale University