You talked about grain, but grain is on the earth. If your truck breaks down, you're safe. But when you're on the water, you may have to travel for hours on a bad sea. It's not the same principle as being on the ground, on the side of the road.
There's an issue of safety in having a small craft harbour in a place where you can easily access it. If you take that away, well, you put a life in danger.