Self-driving car senses objects and must make difficult decisions: Is this radar reflection from stationary light pole or from a moving object? Is this a parked car or a moving car? Will this pedestrain/biker jump on the roadway? What if the car next to me going to turn left sharply?
No such thing exists in the air. The air is mostly empty, there are no stationary objects next to the route. If there is a building, aircraft can fly as far as 500 meters away from it - try finding a driveable road with no obstacles at that distance. There is no people or large animals. There is not even curb to hit.
Importantly, I bet there are no legacy vehicles in the approved routes - and I am sure they will have some sort of V2V tech to ensure that all objects in the air will transmit their position and intention.