There's something you seem to be overlooking: insurance does not cover any/every cost. Every policy has a limit. The legal minimum for liability (property damage) in most states is ridiculously low, $15k or 25k. That's the most the at-fault person's insurance will pay. (Of course the at-fault individual could be sued for the difference, but that rarely happens.)

The owner of the Tesla (in this case) has their own insurance that may cover all or part of the difference. But there's a limit there as well, typically the market value of the car. Which is why cars get "totaled", meaning the cost of repair exceeds the value of the car. Insurance only pays market value, not repair cost.