2005 - As part of the 'Bankruptcy Abuse Prevention and Consumer Protection Act' student loans from for-profit and non-governmental entities were given immunity to dismissal in bankruptcy. [1]
2012 - College enrollment flatlined. [2]
It's basic supply and demand. The widespread deregulation of university tuitions paired with lifelong debt even from private creditors removed all cost barriers to education. And so the only weighting factor in the supply:demand relationship was how many people were willing to take the poisoned fruits of ever-larger life long loans. And so universities kept ratcheting tuition up under spurious justification. Until the number of people entering university flat lined.
[1] - https://en.wikipedia.org/wiki/Bankruptcy_Abuse_Prevention_an...
[2] - https://www.statista.com/statistics/183995/us-college-enroll...
Either those things have nearly maxed out their cost potential, or it's the strong dollar (the dollar imploded during the disastrous Bush years, which sent nearly everything priced in dollars skyrocketing that wasn't nailed down (consumer prices and wages were largely nailed down)).
Might be a combination of those things. The average student debt acquired for a four year degree, has been nearly flat for six years, after soaring from $20k to $30k in six or seven years (between the years '05-06 and '11-12). This six year span is the longest period of flat growth in individual student debt accumulation in a quarter century.