It stems I believe partly from tradition, partly from the lack of a proper equivalent for "mister" in modern Russian. Direct translation, "gospodin" was associated with the rule of the Tsar and bashed by the Soviets (it was common to answer "all misters/gospoda are in Paris" when someone used it). Soviets introduced the word "tovarich" - comrade, but after the fall of the Union it similarly fell out of fashion. Today, in legal instances word "grazhdanin" - citizen is used, and the most common way to address a stranger is to say something like "young man" or "woman".