because water is more treacherous and a smaller domain of control (as in, it's more complex, greater unknowns, etc) than having cubic kilometers of open air tha

because water is more treacherous and a smaller domain of control (as in, it's more complex, greater unknowns, etc) than having cubic kilometers of open air that you can fly through. Think about it, 2D plane, tough medium that has low visibility, can hide many things. Tides, currents.. EVERYTHING has a potential to be a difficult maneuver / emergency situation. Just because it was an earlier mode of travel doesn't mean it's simple.