A: Air travel generally is a far simpler problem to solve, because there's national standardization of the air navigation system, the airport paint and signage, and very clear rules of separation with very few edge cases. And yet we do not have anything close to self-flying planes no matter how much money you throw at it. And we're not even close to getting there. Whereas with cars, none of that is true, municipalities get wedged into violating their own equivalent of human interface guidelines all the time. Worn paint and signs for years, busted cross walk signals, confusing intersections, human driven cars that consistently do not follow the rules but in inconsistent ways.
B. Personal air travel has a significant regulatory burden in the transition from ground to air. The ground is city + state regulated. And immediately once airborne it's FAA regulated, but not under any kind of Air Traffic Control, as almost all airspace below 1200' above ground is uncontrolled. So ATC has nothing to say about it, and no central mechanism for negotiating conflicts.
Where are you allowed to takeoff and land is easily figured out today: airports only. And that's because it takes all kinds of things into account like obstruction clearance, noise abatement, anticipating engine failures and crashes. We can't even automate commercial flights - it might seem like it's more correct to say we don't automate commercial flights, but we could. That's not really true. The amount of changes to the air traffic control system, and on-board equipment for airplanes, is presently so cost prohibitive that it is effectively a "cannot be done".