I think it's more likely that they have become so big that they are having problems with suppliers being able to meet the day to day demand of products....While they historically are supposedly offering lower prices, in order to keep shelves stocked at an efficient and cost effective level, becomes a problem when all the logistics are considered...
I'm familiar with one bottling company that supplies a lot of their products and have witnessed one of the production lines that begin with a small plastic tube that is heated, blown into a 2 liter size, cooled, filled and capped for palletizing at a rate of several thousand units per hour...The line, in operation, reminds me of a chain gun on a gunship...
The time of the start of production until the pallet is ready for loading on a semi is phenominally short and the company is having a hard time keeping up with demand orders..Then there is the travel time for the trucks to get to the distribution centers...
After a few of the previous shenanigans that Mr Sam pulled on some suppliers in years past, where he contracted for X number thousand of shirts at a given price and the suppliers took out loans to expand to meet the demand and then when the contract came up for renewal, Mr Sam would only pay his offered price (lower than original) and the supplier was stuck with a large loan to pay and wound up closing down due to Bankruptcy....Not too many suppliers these days are willing to fall into the same trap...Years ago, it was reported that Mr Sam went to tire companies wanting to line up a supplier for a WalMart brand of tire, but no one would get into a contract, fearing the same outcome as the shirt supplier...He would up reportedly buying General Tire, or a large portion of it, and that's why the Tracker II tire can only be found at WalMart or Sam's Club..
Many suppliers are not willing to go out on a limb financially when dealing with WalMart and they (WalMart) may be hitting that over expansion point with regards to suppliers..
If you spend any time wandering around their stores, count the number of employees in the whole store that are servicing the floor goods...I understand that they have gone into a restructuring program that has reduced the number of people and therefore their flexible payroll costs...
Then there is the whole board of directors problem when you consider the practices that Mr. Sam used to utilize when he was alive and the attitudes of the controlling board now...Big difference...It's very little about the decision not to sell ARs...