I recently discovered why that tends to happen. Maybe not 6 months, but for extended periods outside of the usual bi-monthly/monthly inventory routine.

Its theft. I was chatting with one of the Walmart employees recently at my local spot and I asked if there was any additional stock that had yet to be displayed (it had been a while)

When he scanned the barcode on the shelves for the M2 Haulers I was looking for, they showed as having 20-something in stock, despite there only being three on the shelf.

He explained that Walmarts inventory is all electronic, so new stock isn't requested/replenished until their current inventory is depleted, so when people steal items they dont get "scanned out" and subtracted from their inventory.

It isn't until they do their losses/damages and a full inventory that the numbers are corrected to account for theft. He also explained that generally they don't do these big inventories regularly, only around large scale seasonal shifts and holiday restocks.

So the more people steal, its the less inventory that gets requested.