Remove this "free money guarantee" and watch how market corrects itself. When students can file for bankruptcy and/or the debt is not guaranteed by Govt, lenders would now use the same criteria they use to issue credit cards to 18 year olds. Hint: It's tough to get your 1st credit card if you have no credit history in the US and most lenders will not even entertain that idea. Some will do if you put in a collateral like $500 of actual cash deposit to guard against the default risk.
When lenders stop lending or get strict, colleges will have to consider how quickly and by how much they keep raising costs.