In commercial terms, interchange fees serve the purpose of rebalancing incentives between issuers and acquirers and, to the extent that the fees are passed on to end users, between cardholders and merchants. In mature systems with wide coverage, merchants may have little power to decline cards, regardless of cost.
If so, the main decision-making power over the choice of payment instrument rests with the consumer, who typically benefits from reward points funded by interchange revenues. The higher cost cards (from the point of view of the merchant) are also those that tend to offer the highest rewards to the cardholder.