No one is demanding that these students go to college; no one is forcing them to select their fields of study, or finance their education via means of student loans. There are simply too many variables of which the college or university has no control over; e.g, the number of times a student changes degree programs, the amount of "waste" in how a borrower may use their student loans, the student's willingness or ability to enroll in a degree program with a better employment outlook, etc. It might even come down to something like "relocatability" -- is the student willing to relocate to a different geographic area upon graduation, if it meant better job opportunities?
You threaten to employ a pretty heavy hand for a situation that could work itself out in a more private, free-market solution. Accreditation is suppose to speak to academic standards set by a university, not the financial aptitude of its students.
The student loan providers would then demand the same things I talked about, as a pre-condition for granting loans to students of that institution. Colleges who had too many defaulting students would be "red-lined" from having their students be eligible for loans.
Or the college could issue student loans themselves, out of their endowments.