There is some nuance. Merchants are permitted to surcharge credit card fees, pushing them on to the customer. Some of course will pay this fee for the fraud protection, but large merchants (like Walmart, who publicly commented on these fees as part of the FedNow comment period [1]), will push customers towards the cheaper rails. Incentives, like discounts, matter, especially at volume.
There are some merchants I'd absolutely want the fraud protection for, but most merchants I interact with I'm fine without and not paying a credit card fee pushed on to me to have. People drive miles to save a few cents on gas, so 3% savings is not trivial to a lot of folks. I admit it'll be an interesting natural experiment to see how volume shifts across systems, but UPI and PIX provide some evidence as to how it'll play out.
[1] https://news.ycombinator.com/item?id=36012866
> Walmart has observed a severe misalignment of incentives that has plagued the payments system in the United States for decades. Certain incumbents and large participants enjoy massive profits by stifling innovation in payments, ensuring that account access is limited to a small number of networks, and perpetuating barriers to entry for alternative solutions. Controlling this access allows the dominant players to extract rents from other payments system participants, ultimately resulting in higher costs for all consumers, particularly consumers who are unbanked or underbanked.