Just tossing a guess, would love for someone who actually knows to chime in though: in their language they're probably taught to refer to strangers with the respective word for "sir" as a formal construct, so they apply the same to English even though the culture is different, because they will probably be taught this way as sometimes happens, school teachers don't actually pass on the cultural uses/ways of talking of the countries where the language is spoken alongside the language itself, so it's easier to stick to plain translation in some cases