The common reason here is that among people who aren't the sort to post on Hacker News, knowledge of how to change these things -- in the operating system for l

The common reason here is that among people who aren't the sort to post on Hacker News, knowledge of how to change these things -- in the operating system for locale, in the browser for preferred languages -- or even knowledge that these things can be changed, is uncommon. See also: "you can't fix the user".