Here in Germany, a lot of retailers/restaurants either only accept or massively prefer the local Girocard system and won't accept foreign cards. E.g. a Czech colleague not so long ago failed to pay with their Czech Visa (don't nail me on the card type, may have been Mastercard but definitely was not Amex).
I mentioned in the other comment why being unbanked is an issue.
Also, let me tell, that I pay conversion fees and other random shit even in places like Denmark (which uses DKK not EUR) with my Maestro card.