Let me tell you a secret about Walmart.....some of you probably already know this. WM treats most suppliers......let's say.... not well.
In some cases these suppliers operate on short term cash flows. This means that many of them cannot send inventory to Walmart until Walmart pays them for previous shipments that Walmart has already received, sold, and has profited from. I have seen this on everything from apples, to window cleaner.
Be aware of this the next time you shop there and they are out of stock of some item that is available everywhere else.