> The first one is just an hidden tax and garbage profits made possible only due to the monopolistic behaviour of credit card companies.
I'm not sure any supposed monopoly is necessary here to explain anything. In fact, there's no monopoly and different competing issuers have different levels of fees and 'rewards'. Eg American Express explicitly has high fees and high rewards, and competes against Visa and Mastercard (and against domestic systems in eg Germany or Japan).
A monopoly (or oligopoly or cartel) argument could perhaps explain why the smallest fees you can find are still 'high' by some arbitrary standard, but it couldn't explain why American Express is a viable competitor.
From my understanding this cashback systems come from two sources:
(1) Money taken on processing fees on Merchants themselves.
(2) Money taken from the interests of debt from the people screwed by this entire system.
The first one is just an hidden tax and garbage profits made possible only due to the monopolistic behaviour of credit card companies.
The second one is just plain simply immoral.