Costco is membership-only, so everybody shopping there is strongly incentivized to do so bearing the payment methods they accept. A random corner store or onli

Costco is membership-only, so everybody shopping there is strongly incentivized to do so bearing the payment methods they accept. A random corner store or online retailer does not have that luxury; they have to accept whatever their prospective customers have on them (and to a lesser extent prefer, if they have multiple brands' cards).