I mean, why do (some) Americans think that every country uses US Dollars?

Post WW2 the US economy was the only one that hadn’t been bombed to absolute shit…

So the US dollar was worth more than any other currency. Exchange rates fluctuated constantly, but US was always worth it. So US travellers could “haggle” in US currency, and even if it wasn’t enough at the moment, it might be too much tomorrow.

The assumption in areas with US travelers, was shop owners all kept a stash of US currency to exchange when it was highest.

So you got some elderly travelers who think the world is still like when they were teenagers, and some younger travellers going off decades old information.

For the host country, it’s a steady stream. But very few Americans cross either ocean, which is why it’s often people on their very first trip who have no idea what’s happening. They learn as soon as someone actually explains it, but everyone is so tired of the steady stream they don’t keep explaining.

It’s the exact same thing with Chinese tourists going to America or Western Europe.

The few who do it regularly, quickly learn to blend in, it’s just a constant stream of people who just showed up and have no idea what the actual cultural norms are due to language barrier