Idaho is pretty sparsely populated and mainly rural which leads to lower car insurance rates. According to World Atlas, Idaho has the seventh least population density in the country. There are roughly 20 people for every square mile. Wide-open spaces with few people mean fewer cars out on the road and fewer accidents, everything an insurance company loves.
Auto insurance is financial protection, and not just for the investment you made when you bought your car. After a really serious accident, bills for damage and injuries can easily reach into hundreds of thousands of dollars. If you happen to cause such a wreck, the victims could sue you. In the worst case scenario, assets such as your savings and home could be seized.