Europe is artificially capping the interchange rates - that doesn’t mean that’s the market price for that service.
As for America, there’s 4 card networks, and no explicit regulation preventing you from starting another (just the huge regulatory burdens involved with any money-processing business, PCI, etc).
If they were charging so much more than is “justified”, couldn’t one of the dozens of well-funded players in the fintech space swoop in? Couldn’t Walmart fall back to cash and a “Walmart card”?
Instead, we see even goliaths like Walmart spending money and time to support newer features like tap to pay because it reduces fraud losses and customers just prefer it.
The “justified” thing is silly - is Apple charging more than is justified because they make a profit?