Apple Card

Apple's whole shtick is image. American express is viewed as a "premium" credit card company. So they'd rather go with a company (like Goldman Sachs) that gives off that "premium" vibe.

I've seen memes where people who own American express cards are, effectively, calling the other card brands (citi, capital one, chase) one of the poor's cards.

Simplified, Apple should just grit their teeth and go with a bank that will accept them, such as capital one or citi. However, they should do so on their terms (Apple gets whatever cash back options that they want but compromise on APR or some other variables).