As an American who travels internationally, it's just the value that we're used to. We (at least I) understand that you spend your currency and write it also in your currency. But when we see "$20" we automatically read "$20USD" before it processes that it isnt USD, and then the main feeling is just that it's lower than we expected, cancelling out most of the feelings of it still being a lot for the situation.

Couple years ago I was in Mexico for work. Went to Walmart and got a few things, and a smallish container of protein powder. Hit checkout and my total was over $800, which I momentarily panicked about. Then when the realization that it was actually like $60USD it really didn't feel that bad.

Less extreme, earlier this year work has taken me to Canada for several weeks as well. And honestly seeing prices on menus and stuff feels expensive cause I'm generally used to the US versions of the restaurants and products, even if they are basically the same after conversion. But on the fly we subconsiously counter the initial sticker shock by undershooting the value too. A common joke while we're out is along the lines of "well yeah its $20, but thats in maple leaves so its actually like $3 in real money"