Car is insured but driver is not on policy?

If a car is insured by the owner of the car but the owner lets someone else use it without adding the person to his or her policy why does the driver still count as insured?
And whats the point of being able to add someone to your policy as a “primary driver” if others count as insured without being on the policy because supposedly “the insurance follows the car”?

Register New Account
Reset Password