Their no fee cards are not their primary card base. As a vertical provider, they simply charge merchants more, and use that money to look after their customers more so than other majors. In general try to do a charge back with Amex vs other majors and watch what happens. Amex usually screws merchants more much than other payers, at least in APAC and EMEA. I don’t know American markets as much but I assume the model holds true.