This is always an interesting subject. I'm reminded that someone made the observation that if you try to spend Canadian currency in the US, away from the border, the response is as if you were trying to pay with Russian rubles.
The greenback is a 'world currency.' The loonie isn't, plain and simple.
You'll see the same thing in Europe. If you attempt to spend euros at a small town in Wales, they'll likely be accepted. Swiss francs? Probably not.
Why? Because the euro is another world currency.