Costco is one of the rarest companies that, by corporate policy, has a cap on the profit they make on products year over year.
They choose to do other things once they hit that cap, like negotiate lower prices from their suppliers or, in the case of their chickens, fucking create their own chicken processing plant to vertically integrate the costs.
To terribly paraphrase their CEO, "Raising prices is easy and addictive. It's much better for our customers if we take the time and understand why we're losing margin and try to fix that."