Here's a scenario I come across a lot: debtor finances a car, then drives around without insurance and the car gets totalled. Then debtor says "why should I keep paying when the car is wrecked?" Why?
The finance company did not sell the vehicle to you, they financed it. They spent money out of their pocket so that you could have the car. If your loan was for $12,000 then that means the finance company cut a check to the car dealer for $12,000 on your behalf. You owe it back to them, whether you have the vehicle or not.
The car is simply a form of security pledged against your promise to pay the loan back. If you default, the finance company takes their chattel and sells it for whatever it is worth at auction. Whatever they sell it for is applied to your balance. If they sell it for more than you owe on the loan, they give you a refund. If they sell it for less than you owe, then you still owe the remaining balance.
Put yourself in their shoes. Suppose you have a "good" friend who wants a car. You agree to loan him the money and you cut a check to the car dealer for $10,000 to cover the purchase; the car dealer puts your name on the title as a lienholder but your friend is the legal owner. Your friend pays you back $1000 then stops paying (he still owes you $9K). You call him several times and he doesn't return your phone calls. You may start to worry that he won't pay you back. Several months go by and he still doesn't pay you a dime. So you stop by his house one day and take the car. ... Turns out he's had a few fender benders, spilled soda all over the seats and carpet, broke off the turn signal lever, hasn't taken care of the car ... you can only sell the car for $5000. Would you want to lose $4000 "just because he doesn't have the car anymore?" Wouldn't you want break even?