I'm not affiliated and may not know what I'm talking about but ... the drones we're currently flying are programmed with a set of GPS waypoints, and assume uninterrupted airspace between those waypoints, avoiding collision with the ground by gaining altitude. Self-driving cars have the advantage of a map and can assume a reasonably flat road surface.
Imagine how complex the path planning would have to be for a robot like this to successfully climb and descend a rocky mountain ... not only would it have to plan where to place it's feet for balance, but it would have to look much farther ahead to avoid walking/running into dead-end paths.