Regulating things like this is the job of governments, not payment middlemen FFS, so Visa and Mastercard very much share that blame
It's in Australia, a democratic country where capitalism at least partially a thing, and Mastercard and VISA are international companies, meaning just because one country does have such system, won't mean everywhere does. But to gain profit and because Steam and Itch are also international. They have to either ignore (losing customers as well) or enforce it (keeping customers happy and letting them fuel their money greed), never expect a company like that to just ignore it btw