"From October, Mastercard said it would increase these fees to 1.5% on every transaction, up from 0.3%. The EU introduced a cap on such fees in 2015 after concerns they pushed prices up for consumers and unfairly burdened companies."
"Mastercard is implementing the rises simply as it's no longer bound by the restrictions imposed by the UK being in the EU."
Thus proving the caps were indeed necessary. If MC was making money with a 0.3% fee the other 1.2% are pure sweet profit margin.