One of the commonest depictions of elves are as incredibly long-lived humanoids, sometimes utterly immune from death of natural causes. They are also more graceful and more coordinated than humans, and incredibly good at archery.
These last two depictions could be related to their long lives. After all, spend enough time doing anything and you're bound to become excellent at it, and that includes putting an arrow through someone's visor at three-hundred feet. Even assuming that, it seems like not-dying-of-old-age would result in a significant population advantage and a superior ability to manage information and history.
Basically, why wouldn't un-aging elves be the dominant species in settings with humans?
Examples of this situation from other works would be appreciated.