Why couldn't they be from trucks from other shipping companies going to the Amazon warehouse, or from other distribution centers presumably located in the same

Why couldn't they be from trucks from other shipping companies going to the Amazon warehouse, or from other distribution centers presumably located in the same general area? I think people may be under the misapprehension that only Amazon trucks leave bottles of urine on the side of the highway. This has been a practice for many, many decades. And not just commercial drivers, either. The word to look up is 'trucker bombs'.