A company that owned a tract of land believed to be rich in mineral deposits contracted with a licensed excavator for the removal of soil from the property and delivery of the soil to the company’s laboratories. While one of the excavator’s trucks was on the way to the laboratory, the rear gate broke loose, dumping three tons of soil onto the highway. A motorist who was driving a short but safe distance behind the truck was unable to stop in time and collided with the soil, causing her serious injury. The rear gate had been negligently secured by one of the excavator’s employees. If the motorist sues the company for his injuries and does not prevail, what is the most likely reason?