Higher costs of compliance in the EU perhaps?
I don't see how that is dumb, the EU cannot do anything about issuers outside of it, and PSPs have to reflect the huge difference in interchange fees one way or another.
The only businesses suffering from the cap are issuing banks.
Some countries smaller than the EU bloc have more complex regulations regarding online payments.
The EU managed to cut fees in half for its population and businesses, if you want to stay outside then why do you care?