“Walmart I can understand.”
One of the clerks at my local Walmart said that soon as they get some .22 in it happens: First guy spots it; out comes the cell phone; in a short while the shelf is cleared.
Some of it is the “buyers” for the gun shop in the next town over.
Walmart likely runs out fast for the simple reason they likely only order small amounts to start with. Whether it's ammo or tooth paste Walmart keeps limited on hand inventory. They don't care if they can make more money. The ones in Bentonville who control how much of any item any of their stores or warehouses can have on hand operate on an On Time Inventory System. They are their own worse enemy. They would rather keep minimal items in stock and low inventory cost than have more sales keeping items fully stocked. They went to that type of system about five or so years ago. In my local Wally World they didn't have motor oil for several weeks one time.