Since Walmart keeps popping up in other comments, I'll do devil's advocate using the exact same argument other people used:
If you don't want to buy on Walmart and their custom payment system, then just go to a competitor.
With that said: this is an unrealistic scenario. Walmart doesn't pay the famous 30% to ApplePay, only a regular CC-like fee (probably less). Also, physically they can just accept contact payments where they don't interact with Apple but it still works with the iPhone wallet. Online, they can just use credit cards instead of ApplePay, which iPhones have autofill for, and probably not lose much.