Since we're all assuming that the retailer under discussion is Walmart, I'll give my observations. Whoever is in charge of ordering guns and ammunition for them is an idiot. From what I've understood from people I know who have or do work for them, someone at the corporate level decides what and how much of any product each store gets.
Just the other day I walked by the ammo cabinet to find it stacked full of 7mm Mag, .300 Win. and WSM, .30-'06, and the like. Some "Deer Thugs" logo or something on all of it. I don't think they've sold a box. You can't tell me that the LGS down the road that's a one man operation run out of a 70's model single wide trailer gets priority over Walmart. He is currently having no trouble coming up with 5.56, 9mm, .40, and .45. It ain't dirt cheap or anything, but it's available.
So here's what I think: the people in charge of getting product for the stores don't know crap from shinola when it comes to guns and they're ordering whatever they can get for cheap and shipping it to stores not knowing the difference. That's the only explanation I can come up with.
'Merica: Back to back World War Champs