I assume they’re secured loans, so the lenders would rather repossess the cars in bankruptcy and sell them themselves rather than support unsecured holders. If not secured, I have no idea.

Bankruptcy is a legally standard way of doing that. Chapter 11 can result in creditors being forced to take losses.

I'm guessing they probably get very good deals on the debt to begin with, (even a consumer can often get 0% on a single car) but bankruptcy will definitely restructure that debt at a minimum.