I wonder if the price increases are simply evidence of normal price discovery in a capitalist environment. Perhaps they were “underpriced” in the past compared to what the public believed they were worth. The fact that so many people keep paying the higher prices indicates that many people believe they are worth the money. However this is only true at the top tier schools. Below that, private colleges need to heavily discount to induce people to attend. It seems like between 30-40k is the price that the majority are willing to pay for private schools on that second level. The top privates could probably increase the sticker price substantially and still attract a large number of qualified full pay students.
Price increases at public universities have far more to do with the tax base’s unwillingness or inability to fund education. In my personal opinion, this is a huge mistake and a moral failure. But thats just me.