"American Express says the deal ended for purely economic reasons, and I suspect that’s right. I’ve suggested that as costly as it was for American Express to lose Costco, it would have been more costly to retain Costco. As big a win as Costco is for Citibank and Visa, it’s a deal afflicted by the winner’s curse because Citi/Visa had to overpay to secure it.
Nonetheless, losing the deal is a big blow:
10% of American Express cards were co-brand Costco products.."
Bloomberg ran a long piece purporting to tell the story of how American Express came to lose to Costco co-brand deal, and along the way details the challenges American Express faces to its business model. It begins with narrating the cultural differences between American Express and Costco and...
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Citigroup actually did relatively well afterwards. Costco membership enrollment increased over time, as reported in the media, and so did the Costco Visa applications, as well as Citi crossmarketing to the Costco customers its other Citi cards.
Outside of the 2%-4% cashback areas, the 1% cashback area that Citi Costco Visa offered can be made up by applying for another Citi credit card that paid at least 2% back instead. It's a win-win for Citigroup.