Almost all transportation whether railroad or trucking send JIT(Just in Time) loads, what is ordered by large companies use to fit on full 53 foot trailer of same products of one company, but more and more companies are using LTL(less than truckload) as you will see trucks pulling two mini trailers that might have different brand names. Companies don't want to store excess cause they don't want to pay rent on trailers, and rather keep monies in their coffers. Walmart, other than Holiday season, has often has much less than well stocked shelving for couple reasons, less is better as they believe people will buy regardless as they have usually discount prices, but I think it is to hold down employee costs. Why have full shelves that have to be straightened each night if you have less goods. But where they have really gone downhill is fresh veggies and fruits, doesn't last long and looks horrible. Grocery has least profit margins but they draw you into shopping for other products. Target added grocery to some of their stores, don't know how they get anyone to buy as prices are not close to discount.
It is getting a bit like when USSR was around and government control, short supply of foods on shelves, and if you saw extra you took it if it was not a coupon item, long lines at bakeries didn't happen cause they had best bread, it was a coupon item and you couldn't hoard.
This is how supply controls demand, reduce the amount and people will get itchy of companies running out. LOL, those who live where it real icy, you go to the store and even though you have couple bags of salt at home, you buy the last bag on the shelve? As soon as you leave, guy in back brings out 2 bags, ROFLMAO.