I think the counterargument to this simplistic assertion is that "The boy was hit by a ball" seems equally legible to me to "A ball hit the boy". If you're quickly reporting the details of an accident to a doctor and it's crucial to get the information across quickly, I think many speakers would still start with "He was hit by a ball", not "A ball hit him." We're not interested in assigning agency to the ball here, we're interested in the effects on the boy. We're focusing down on the boy first, then talking about what is happening. Is he hitting a ball? Getting hit by a ball? Nobody cares what the ball's doing, it doesn't need to be prepped for surgery.