Car insurance companies all have their own formulas for evaluating risk, and while some of the factors are known, others are industry secrets. We know that all auto insurance companies are going to charge a little more or less based on things like gender, age, make and model of the car and the neighborhood you live in. But there are also points of data that some track and others don't, and points of data that we really have no idea whether or not they're tracking.
Some of the known factors seem a little... indirect. Certainly, moving violations give us a sign of a driver's habits on the road, but why should credit score matter?
Multiple studies have confirmed the findings that a low credit score correlates with a higher probability of the auto insurance company taking a hit on the policy. Those losses will tend to be much higher than the losses taken involving drivers with higher credit score. Further, someone with poor credit is less likely to pay insurance premiums on time.
There are several reasons for the correlation. Someone with poor credit may be neglecting important maintenance on their car. They may show a pattern of irresponsible behavior. They may even be more likely to file false claims. This is not to generalize about people with poor credit, only to say that people who exhibit this sort of behavior are likely to have poor credit, and insurance is a game of statistics and probability.
If this doesn't seem entirely fair to you, there are plenty of people involved in the industry who agree with you. This data first came to light around the turn of the century. Right before the United States went through a period of being hit with one major financial crisis after another. Twenty-five years ago, poor credit typically pointed to poor financial decisions. Today, not necessarily. In California, Hawaii and Massachusetts, the practice of setting a person's rates by their credit has been discontinued.
If you're able to fix your credit, you should fix your credit. Beyond car insurance there are simply too many benefits to a high credit score to count. Otherwise, it might not be a bad idea to take a defensive driving course in order to offset the bump in your premiums.