Its obvious a huge part of the loans are used for careers that will never make its money back, and the loans only collateral are the person itself(not his parents assets). So if someone had an arts degree that cost him 150k, and never made that money, he should be able to default on that loan. As he does that, colleges have a strong incentive to keep tuition matched with the income produced by that degree.
My understanding is that college loans have a special protection by the government that makes them undefaultable. Dont subsidy college loans! Dont take more money from all(including under represented poor people) to put it in the pockets of colleges. Just make the loans defaultable, and you will see such a massive movement of defaults that colleges will never put unpayable debt ever again.