The us is different between the us and Europe, everytime someone uses a credit card there are fees that go to the bank and the credit card processor.
In Europe these are legally capped, in the us they are not. So the 2% cash back on US cards is the cards and banks competing for market share by providing kickbacks from these fees to customers.
https://www.bitsaboutmoney.com/archive/how-credit-cards-make...