1) Some companies are more aggressive in certain areas and for certain people. Some carriers are more willing to insure certain risks then others (certain drivers, writing in certain areas, etc) so they offer lower prices. Some carriers are the opposite and don't really want that type of risk.

2) The policies carriers can issue can be highly modified. This is the part that no one sees until they are in an accident and by then they have been paying premiums already. Some carriers don't modify policies very much so they actually offer much better coverage. One quick example: the standard ISO policy does not exclude coverage for carrying property for hire. I found out a few years ago that Progressive's policy does exclude this coverage. By Progressive excluding this coverage their over-all exposure is less so they can decrease their rates slightly.

3) The carrier cuts corners where ever they can… usually in the claims dept. So you have inexperienced adjusters trying to do way too much work. Call these carriers and you will never be able to speak to an adjuster. Also, the claim take much longer to process. Again, you don't know this until you file a claim and if your filing a claim the carrier probably wants you to drop the policy.