The main benefit of boats over planes is that they require less energy to move cargo. However, they also more effectively amortise the cost of labour involved i

The main benefit of boats over planes is that they require less energy to move cargo. However, they also more effectively amortise the cost of labour involved in moving goods. So drones make more sense in the aeronautical space because they minimise labour in an area where it cannot be effectively amortised and decrease the amount of energy required to move stuff around (no need to lug a few humans along with the cargo).