Generally, the cost of college tracks inflation. It's where the funding that is changing that makes it appear to increase. 40 years ago state funds paid for most state college costs (hence the name, "state" college"). Now, most states are broke and rapidly withdrawing most of the funding support from their universities, shifting costs to the students.

Administrative staff costs are rising as well, but the tenure track professors are expected to do less and less administrative work, theoretically allowing them to teach more classes. I don't know how much this works though.