Supermarket Question

There are three supermarket chains in my city. Chain A (okay it’s Safeway) never stocked Stewarts Ginger Beer.
Chain B stocked Stewarts Ginger Beer for a year, after I decided Chain A was crap and generally overpriced, but Chain B stopped carrying the product.
I’ve recently discovered that Chain C carries Stewarts Ginger Beer!

I know that Chain A doesn’t carry braunschweiger or liverwurst, even at the deli, for some bizarre reason so they must have equally bizarre reasons for what they do and don’t keep in stock.
Chain B says their distributor discontinued Stewarts Ginger Beer and just produces the other products.

How the hell do supermarkets work when it comes to distribution and what it keeps in stock? Stewarts is the same darned company! Are there three Stewarts bottling plants who decide what to make and what not to make and have exclusive contracts with each supermarket?

I haven’t worked in the grocery biz, and hopefully someone who has will stop by shortly, but: a distributor isn’t the same as a manufacturer. I would assume that rather than deal with every individual company whose products they sell (which must number in the hundreds, if not thousands, for a good-sized grocery store), they buy their products from a middleman distributor who deals with the logistics for them. Larger chains like “Chain A” might have their own “in-house” distribution channels, but smaller chains might not, and mom-and-pop places almost certain use a third party to get their products.

Sometimes it’s items that just don’t sell. Other times, an item from a certain supplier is not carried to highlight a similar product from another supplier that may be more profitable/cheaper. Individual stores don’t have much say in what and what doesn’t get carried, MOST of it is done at corporate level. If a new supplier wants to get on the shelves, he has to “cross the palm”, usually by giving the first stock-up to the store(s) for free[a huge outlay]among other goodies to the powers that be. The bigger the chain, the more leverage can be applied. And other times, we have no frickin’ idea what’s going on.

I’ve had some success with simply asking the supermarket manager to carry a product that I don’t see stocked.