That's because liberals assume the legitimacy of the creditors' rights. Populists are not always so ready to grant this. After all, bankers are not usually poster-boys for populist movements of any stripe.
At least progressives should absolutely deny the legitimacy of creditor rights. That seems to me elementary. And, in the meantime, why not be sanguine about debt. From a personal point of view, as a two-time bankrupt, I have never overly estimated the perogatives of my creditors, and it has worked out very well indeed. (I declared bankruptcy last, by the way, about three years ago, and today I have two excellent credit cards.)
Quincy