Zipcar is fail because you pay as long as the car is away from its original "home" parking spot. Why can't I drive it to another Zipcar spot in front of the mal

Zipcar is fail because you pay as long as the car is away from its original "home" parking spot. Why can't I drive it to another Zipcar spot in front of the mall? For example instead of paying just for the 15 minutes it takes to drive there, I have to pay for the drive time plus the time it sits in the parking lot for 3 hours while I shop. Fifty dollars, no thanks.