Visa and Mastercard charge high fees because their dominant market position forces merchants to accept them. Then they use part of the fees to bribe customers with rewards programs.

A new payment network doesn't have leverage against merchants so can't charge the same high fees and therefore can't offer the same rewards programs, but then they can't get consumers to use their card, which is what they would need in order to get any leverage.

The rewards programs are a grift. The price of everything goes up by 3% and if you get a rewards card you get 1-2% of it back, therefore you get one. Then you're still out the other 1-2% you wouldn't have been if the market was competitive, the people who don't get one get punished by being out the entire 3% (which inhibits competitors with lower fees), and Visa and Mastercard suck billions of dollars out of the economy into their Scrooge McDuck money bin because consumers have been defrauded into thinking this arrangement is to their advantage.