They aren’t dischargeable in MOST cases, but there have been a few judges recently who have discharges large Plus loans.
And not being able to discharge the loans doesn’t mean they are being repaid. There is a large amount of loans that haven’t been repaid and won’t be. The borrowers may ruin their credit scores and be unable to buy a house or get a credit card, but that doesn’t mean the government as lender has been repaid. Taxpayers are paying.