At this point, only 16% of undergrads attend private schools. So we're talking about a subset of Higher Ed. There are reasons why they have jacked up tuition,
but they are private entities, so they're not compelling anyone to attend. The important thing to consider with privates is this: they have jacked up tuition well above the actual cost of attendance (i.e. tuition is MORE than the cost per student). If I had to guess, it's because many of these schools maintain a need-blind admission policy.
This article is old but you'll see all the cost drivers examined:
http://www.nyu.edu/classes/jepsen/costreport.html
This article puts the report into context:
http://www.highereducation.org/crosstalk/ct0598/voices0598-ike.shtml
I can't find the article now but one of the commissioners called for examining whether private institutions should continue need-blind admissions policies since they were considered by him unfair to families paying the full rate.