One vacation in a European country my credit card simply didn't work due an error made by the bank (which would only have surfaced if I had overdrawn a limit while at home).

One vacation in central america the ATM just swallowed my card - on a Saturday night and it was unclear when the bank would be open again.

One vacation in another country the ATM kept my card and told me it had expired - ok, so that one WAS my fault, but we're already at example #3.

Yes, maybe those are exceptions and people living there are better prepared/have friends/whatever - but I have simply experienced it failing. Cash has never let me down, as long as the other party accepts it or that one time when my wallet was stolen.