One thing that never made sense to me is that im sure 99% of all the rich people who have amex also got at least another card. If you dont take amex wont those people just use another card.
1) the backup is likely a high end rewards / corporate card whose fees are as high or higher than Amex for most categories of spend; and
2) it’s kind of weak for the last interaction with a business be them saying they won’t take your preferred form of payment because they imagine it boosts their margin by .3%.