Because some of the things they buy are imported, or depend on imports.

Unless an American’s income went up by the same amount, they lost purchasing power. The greater the proportion of non-USD assets they have, the greater purchasing power retained (i.e. the wealthy that depend less on selling their labor).

A share of Microsoft costs an American 16% more today than a year ago, whereas from the perspective of a German a share of Microsoft cost slightly less than a year ago. That's one way to look at it, anyway.

The cost of health insurance (in USD) just went way up.