Can someone explain to me why the debt write off % is so high on...

Can someone explain to me why the debt write off % is so high on secured loans?
Surely MNY repossess the cars & resells them on?
Even with a 20% hit on the market value of the car that still shouldn't amount to such a high % on people who are supposed to be credit checked.
I'd hate to think what the % write off would be in a recession.
Do they even have a deal with an auction company such as Pickles to resell the car?