Tribal reservations don't require license plates or insurance usually, and you cab choose to self insure if you have sufficient cash set aside.
Absolutely beg to differ. I was on a high-deductible, low-benefit plan for a two-year old used economy car in Louisiana with no marks on my driving record for $250/month. The insurance cost was more than the monthly cost of the car. That being said, it was more than the state mandated liability insurance, but it still wasn't anywhere near the levels of insurance I now have in Washington State on a brand new Tesla Model 3. As you mentioned, it's highly dependent on where you live, but it's absolutely feasible to be paying $200-$300/month for insurance.
Edit: Apologies to parent comment. This was a reading comprehension failure.
Source: I live in New Orleans.
I think you are ignoring the third party risks - damaging an expensive car or hurting someone. In that situation, you use insurance if you want to protect your money. If you have no money, insurance make little sense, and you just suck up the risks of pranging your beater.