Amazon did try to add that line item and the administration pressured them to remove it. And you are making a very big assumption that either Costco or their suppliers absorbed the cost of the tariffs. Because I don't have a link handy, one study I read said more than 80% of the cost of tariffs came from the consumer's pocket, not the supply chain.
When I say absorbed I don't mean they didn't raise prices. I mean they didn't just transparently pass those extra tariff fees on to customers as a line item. With that increase in base costs they either lower their margins and earnings or they increase prices to keep them in a stable range. They are a for-profit business so it's highly unlikely they'd simply absorb the increased costs and not raise prices. There may have been some initial elasticity where costs rose faster than price rose.
