Self-destructive punishment.
Locking me in a state where I had bad credit meant that I couldn't move in my career. My education was useless because my bad credit wouldn't allow me to be employed in my intended industry. Not only did the government deny itself the money owed, it denied itself years of income tax from me. People who are forced into this state, often suffer from major depression, which has its own set of negative consequences which are all typically harmful and expensive to society.
Of course, the system won't take responsibility for itself. It would rather blame the deadbeat former student, and then file many articles in one (or a few) of the major media outlets, complaining to the general public about how many billions of dollars it had to write off.
I would love to know the real truth about the status of the student loan system. How many truly run from their debt, and how many are unwitting victims of administrative foul-ups?