The Durbin amendment (regulating debit interchange in the US) and its EU equivalent aren't regulating Visa and Mastercard scheme fees, but rather interchange fees, which Visa and Mastercard set, but issuing banks earn.

Of course scheme fees are ultimately at least partially paid from interchange, but lower interchange is primarily a problem for issuing banks, not the networks.

The Durbin amendment in particular was also supposed to foster competition between networks (by mandating each debit issuer to support at least two unaffiliated networks per card), but given that only very few places accept only debit cards, that didn't work out quite as well as intended in terms of bringing down both interchange and scheme fees via market forces.