As a layman, I always wondered: what do Visa and MasterCard even do? They don't issue cards or actually extend credit. Banks do that. They don't assume any transaction risk. Merchants assume it. They don't actually carry any of the debt that customers produce. They don't accept balance payments from customers. They're just "facilitators" but it's unclear what that even means technically. I assume they have a few datacenter that do trillions of little lookups, but is that all there is to it? It seems like the perfect do-nothing middleman business: Insert yourself into every transaction in the world and siphon a percentage of it.
What stops a big bank from doing whatever it is they do?
What stops a big bank from doing whatever it is they do?