You pay for what u get

Vehicle registration fee is a very important state income. Remember what happened to California last year? The then Governor Davis raised vehicle registration fee by up to 300% to overcome the state deficit. (Not even before the new registration fee in effect, he lost his position). It's one of the property tax. Samething if you own a house, you need to pay property tax year by year. If you want ot ask the reason, then it's the reason why you can drive on the road not pay the toll every mile, it's the reason you can get police's help if you have accident or being hi-jacked. Every vehicle owner pay for the road and service they get. Simple.