Competitive pressure. If your can't be fixed or you don't want to fix it you have alternative forms of transportation or you can purchase another one (either at full price or used). Also, many of us only carry liability.

And it's well known that disreputable repair shops will ask you up front how much your insurance is paying you so they can get the full amount.

You don't need to take a gigantic loan from the government and pay the repair companies for their work.