The thing is, education doesn't scale infinitely like that. The bigger the class size the less attention you get from the professor, the less individualized the education is, the more generic it has to be, the lower the common denominator, etc.

And lots of colleges are known for their teachers. You can't always just hire another identical teacher: good ones are rare. At elite schools, they are often even famous and individually important in their field. You cannot scale that.