There are other factors besides yourself that effect your rate. If the area you live in had a spike in accidents or even robberies, that will effect it. If your age group shows an increase in accidents, that will effect it. It's more than just you, it's also about people who share the same attributes or whatever you call it as you.
Also, it's the game they play. They give you a low rate to get you to move, then they increase it slowly every year.