You have never owned a store have you?
They bought truckloads BEFORE the oil price went down.
In addition, what the price per barrel is today takes months to work it’s way through the system of refineries. Unless you wan to burn crude oil in your vehicle.
During the Obama years the demand for ammo exceeded supply for years. Prices rose dramatically, more than doubling in some cases.
Walmart, somewhat surprisingly, did not raise their prices. My guess is that Walmart had long term prices set by contracts with suppliers so they could afford to hold the line on prices.
What I don't think they ever realized is that the disparity between Walmart's prices and the market overall created a tremendous incentive for Walmart employees to buy up all the inventory on the day it arrived and re-sell it for a handsome profit.
A policy that was designed to serve their customers actually deprived their customers of a valuable commodity.
I have heard that the explanation for Walmart's behavior is their whole business philosophy. Walmart figures out what price will attract customers to their stores. Then they negotiate gigantic deals with suppliers at a price decided by Walmart. They don't give the supplier a chance to dictate the price.
The success of Walmart demonstrates that their business model can be quite successful. Inability to quickly conform to market forces is perhaps a key downside to how they do business.