This. They get a deal on buying pallets of the stuff.
I will add: If you're buying steel for waterfowl hunting, don't cheap out on "economy" rounds. Get the best you can afford. Considering how seldom I'm able to get out duck hunting these days, I buy the $1+ per round stuff like Hevi Shot / Hevi Steel. I used to buy the cheaper stuff like Kent back when I'd fire 100 rounds per season. I think I fired 8 rounds this past season.