They don't do this as charity, though: they do this because customer disgust with being nickle and dimed over a hotdog, and thereby the resultant lost sales from their actual warehouse, will do more harm to shareholder profits than they would gain back on selling more expensive hot dogs (and maybe, just maybe, the hotdogs were always a loss leader anyway, to make the trip to Costco to buy hundreds of dollars of groceries more enjoyable to begin with).

They also change things, I notice they don't have the polish sausage anymore, the dog buns are different, etc.

Hotdogs and drinks are probably a loss leader for Costco. What Apple product would you suggest they sell below cost as an enticement to people to make other Apple purchases?

Most of the Apple subscription services (Music, iCloud, etc) would be a perfect choice there.