In some cases different Visa or Mastercards have different fees associated with them, and if the merchant has configured or negotiated with their service providers to only accept cards under a certain fee percentage then just being a Visa or Mastercard is not enough. One example I can think of is the Chase Sapphire Reserve card as that is (or was I guess things can change) a Visa Infinite card and I believe transaction fees are closer to ~4%> or something versus maybe a standard ~3%. I don't know the exact fee percentages but that's the mechanism.
I agree the reality is a bit more complicated and even wrote about it in France when dealing with gas stations but what I wrote is broadly true. You can just take a credit card to Europe and the vast majority of the time you just won't need cash. I also agree it's a good idea to have a couple of cards though and maybe your debit card too. Frankly I do this in the US as well, and not just when traveling abroad.
I agree the reality is a bit more complicated and even wrote about it in France when dealing with gas stations but what I wrote is broadly true. You can just take a credit card to Europe and the vast majority of the time you just won't need cash. I also agree it's a good idea to have a couple of cards though and maybe your debit card too. Frankly I do this in the US as well, and not just when traveling abroad.