that's because selective universities don't _want_ to give degrees through MOOCs at a lower cost as it 1) reduces the value of their degrees, and 2) reduces their reputation.
Top universities could easily increase their student body 2x or 3x, bringing acceptance rate back up to 15%-20%. But they don't want to. Because what they're selling is not just an education (you can get that at (fill in blank) State), they're selling prestige and future opportunities, and the value of that lies in its _scarcity_.