Premiums will change from year to year based on the loss experience of the companies. Coverages such as BI/PD liability, medical payments, uninsured/underinsured, towing, etc. typically go up by varying percentages. Physical damage such as comp/collision almost always go down with the age of the vehicle covered. But the net change in the total policy premium is usually up.
To see what's happening to your policy, you have to compare premiums on an individual coverage to coverage basis.