Additionally, Amex provides both the credit as well as credit card processing for their customers instead of splitting the business with thousands of banks. So

Additionally, Amex provides both the credit as well as credit card processing for their customers instead of splitting the business with thousands of banks. So when a merchant exceeds whatever shadiness threshold is set by Amex they are banned from accepting all Amex cards vs. cards issued by $yourbank. So there is incentive for the merchant provide good customer service.