Most cars being released come with a variety of sensors, a number that feels to be ever increasing. Data doesn't need to come from AI.
The point is that this data would have been collected by the first-movers the entire time they are on the road. Such data would not be made available to newcomers.
If a new self driving car company would join the scene, they would need to gather all this data again themselves, somehow. This is the "uncopyable advantage" mentioned by OP.