There are two hard parts of hazard avoidance: identifying the hazard in the first place, and dealing with large numbers of different hazards moving around. Transponders, TCAS, and maps solve the first problem well enough for boards and airplanes.(there are time where they fail but they are rare enough to ignore). Except at ports/airports traffic is generally light as well meaning drones and boats only need to worry about a small number of hazards which makes this easier.

Autonomous cars are hard because children, and wildlife do not have transponders, and worse have a habit of jumping out from cover right into your path. Killing children is obviously bad. Even though who morally would argue that wildlife don't matter still do not like the damage hitting the wildlife causes to the car.