I think one big issue is much of the cheap debt is loans people have defaulted on. So you have to stop paying the debt, hope for minimal ramifications before it hits the open market, then buy it back up at a discount, assuming you have the funds laying around to afford the discounted rate.

Loans backed by property (e.g., home, car) which can be repossessed tend to not be as heavily discounted. So its really just if you have massive credit card, student loan, or medical debt, and are willing to put up with harassment from debt collectors on the hope that it’ll be bundled into something worth less than your individual debt