Walmart's known for it's ruthless efficiency.
I'll say if ammo orders are being denied, or whatever, it's just to keep the system from getting bogged down in orders that can't/won't be filled. And to keep the managers and whatnot from wasting their time putting these orders into the system.
This is a company that will close a Walmart, and open up a new one right next to it, rather than remodel the thing. And they do stuff like putting in skylights, then automatic dimmers on the store's lights that dim as the sunlight gets stronger etc. to save on the $20 in electricity etc.