We couldn't keep it on the shelves

So there's this weird phenomenon that my wife and I have experienced on more than one occasion here, and that has also been reported to us by other puzzled ex-pats, and it has to do with the policy that merchants follow when deciding what to stock on their shelves. See, we always thought that it was sort of Econ 101 that if you had a popular item, you'd be inclined to continue to stock it as your customers would continue to buy it, and even having it would be useful as it would bring people into the shop where they'd be likely to buy more things. So popular items are ones that you'd continue to order from the supplier, at least in our small way of thinking.

But here, I have the feeling that having to refill the empty shelf space frequently is viewed as a bit more trouble than a merchant had bargained for. So much so that more than once we've seen stores simply stop carrying things that they sell out of rapidly. Lisa has even asked the management at Waitrose whether they were going to start carrying a lovely little garlic pizza that usually flew out of the door. The exasperated manager said no, noting that "they just couldn't keep it on the shelves!" Apparently having full-looking shelves is the point of retail for at least some segment of that industry here.

Isn't this in violation of some sort of fundamental axiom of economic theory? Lisa remembers that you're supposed to strive to have enough units on hand such that you're unable to sell the very last one. Shouldn't that mean these guys should be buying more?

I'd have written this off as an isolated event if it hadn't happened more than once, and to other people that we know as well. I'm not willing to claim that it's pervasive, mostly because I can't believe the general mindset is to minimize trouble rather than maximize business, but it doesn't exactly seem unusual either. Get 'em while they're hot, indeed.