I think you're seriously underestimating how big VISA and Mastercard are. Valve is estimated to be worth around 8 billion , Visa made 4.5 billion in profits Q2 of 2025. VISA makes more money annually than Valve is even worth. Furthermore If we exclude China Visa and MC make up 90% of all online payments. Steam's entire business depends on online purchases. Steam would be thoroughly fucked if Visa and MC dropped Valve.

What Visa and MC are doing is despicable and something should be done about them, but Valve is not in a position to do anything but bend over and spread the cheeks.