Another major push to increasing tuition cost is that a major component of the US NEWS & WORLD REPORT rating system is tuition cost instead of faculty achievement. So Universities post extremely high tuition costs but issue large grants to almost all students just to keep a high rating.
Another driving force is government subsidies. There is a strong correlation between government subsidy increases and administrative and teacher salary increases and tuition increases.
There is generally little required of professors to teach the same subject matter year after year after year for a few hours per week.