On NA there's lots of good 2h/polearm users who rack up massive amount of kills. If I can't beat them in a straight up fight I can turn to cav or ranged. Many NA maps are not cav friendly, so you're back to getting owned in melee. I like winning though, so whats left is ranged.
As well, all the urban /ruins maps in NA encourage people to split up meaning a good duelist is more likely to fight without being ganged/shot at. Which encourages the above to happen more.
So as destiny and korea has said, map selection in NA is a major cause of the amount of ranged.