Cars bought at auction have a salvage title, and they are not repaired to a level that would be considered acceptable by most people. Those cars are usually mechanics projects using junkyard parts and zip ties.

The other thing is that generally, a person is free to buy their car back from the insurance company instead of taking the cash from the totaling. That is when they will discover they can't just send it to a shop and get it repaired for any reasonable amount, plus the salvage title means no one else wants it.