I stated this elsewhere but the Higher Education Act has specific language about when debt is allowed to be sold - they can't just sell it at any time for any reason, and all the terms of the Act would still apply to the loan since in most cases the MPN stipulates as much (since the actual terms of a promissory note can't be altered without consent even if the payee changes). Specifically, they cannot sell the debt if it "result[s] in any cost to the Federal Government". Reassigning the loans to another agency would incur a massive cost since that agency would have to hire new personnel and build new infrastructure, eliminating the possibility of a sale within the government, and a sale to a private third party would made debt validation very tricky for that party since FERPA would prevent disclosure of a borrower's SSN, student ID number (ergo, the account number), and the itemization of the debt without written consent, meaning in that scenario the borrower could most likely* refuse this disclosure, dispute the debt, and win pretty easily.