I'm fairly sure that since the last Alpha, traders attempt to avoid offering a quest again until they've offered all the other quests of that tier within their range. That tends to make quest distances go up rapidly once you've done all the nearby quests of a particular tier.
I believe the quest list resets every three days, when the trader resets their inventory.
So you can reset the quests offered list just by logging out and back in, but you may find you still only get long distance quests (because you've done all the close ones) until the trader does their three day reset.