This would be unfair to students who were frugal and chose a 20k-25k/yr COA state school with the assumption that their debt must be repaid.
Going to college is an investment that you ideally should plan for and weigh the benefits of the education vs the cost. If you don't think it's worth the 20-25k/yr COA at state schools (or whatever ridiculous amount at private schools) than just don't go. It absolutely is, but okay. This is an incentive to make good choices about college and be educated and productive post-college. But cancelling more debt would remove this positive externality.