who actually does this? I'd imagine most amex users probably have a mastercard/visa anyways, and it's not like they're going to switch merchants to save an extra 1-2% on their purchase, presumably when the merchant they chose already have the lowest prices to begin with.
To not maximize credit card rewards means to subsidize others who do. To fix the problem, you have to regulate interchange fees down so that rewards aren’t sustainable and are no longer offered. The problem isn’t American Express, it’s lax financial regulation.
Personally, I fully support the cramdown of interchange fees and the resulting impact on financial institutions.
[1] https://www.npr.org/sections/thetwo-way/2016/06/20/482797151...
I didn't, for several years, until a Visa card came out with better terms (1.5% cash back) than the Amex variant I was using (1%).
Also, some companies provide an Amex Corporate card for travel expenses, and it's less convenient to charge things to any other card.