> fees are for fraud prevention and sanctions compliance

Visa and Mastercard’s pre-tax income margins for the quarter ending on 30 June were 62% and 57% respectively [1][2]. That is $10bn a quarter in absent competition.

[1] https://finance.yahoo.com/quote/V/financials/ $6.33 on 10.2bn

[2] https://finance.yahoo.com/quote/MA/financials/ 4.67 on 8.13bn

Maybe. But the 39 billion in profits visa made last year suggests they make a fair bit more than that stuff costs.