[Arguendo]

He's not responsible for the damage. The dog's owner is. Even if he had insurance, his insurance company could sue the dog's owner to recover the costs, meaning the outcome would be the same (with a few additional administrative costs).

Why should he have to buy insurance to protect against damage for which other people are responsible? Why shouldn't they (or their insurance company) pay for it?

[burroak]

“Why should he have to buy insurance to protect against damage for which other people are responsible? Why shouldn’t they (or their insurance company) pay for it?”
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Because coverage for this exact circumstance was available to him and through avarice he declined. How can he benefit from a decision to spend his money on whatever and then be made whole from others funds. He is a net winner because the damage to his car and his lost wages are covered and he got to spend his C/C cost on whatever he wanted to. He is being paid twice for the same incident.