- Lender "A" is owed $20,000 by each of 2 people.
- Debt buyer "B" offers to buy them for $1,000 each.
- Debtor "C" realises that getting out of her own debt for 5c in the $ is a good outcome, and take up the opportunity to buy the debt herself. "A" gets their $1000
- Debtor "D" realises the same thing, but he has no way to pay even $1000 for the debt, so passes up the opportunity to buy the debt.
- "B" ends up buying D's debt for $1000, even though it's now obvious that D has little change of ever paying it back.
B ends up with debt that they can never recover - not even the purchase cost. This leads to B offering less money for this style of debt next time.
The only reason B was willing to pay 5c in the $ on the original debt is because that aligns with their odds of getting the debt repayed.
Once you create a system which filters out the debts of anyone who has the ability to pay back a chunk of their debt, the debts that end up selling to the agencies are the real rubbish loans that will never get paid back.