The difference is both direct ground contact and fuel capacity. Even if a drone could carry the energy equivalent of a 20 gallon fuel tank with it, it would wa

The difference is both direct ground contact and fuel capacity. Even if a drone could carry the energy equivalent of a 20 gallon fuel tank with it, it would waste the majority of that energy both keeping itself and its energy aloft. Tires and other ground plane vehicles, mitigate the majority of that waste in exchange for increased navigational difficulty (regarding obstacles like buildings and trees but also moving objects like vehicles in its path). The self-driving robots made some sense but only for very local (couple of block radius) delivery.