I think part of that stems from their roots in Tolkien's mythos. At first glance, it appears that elves don't have an evil bone in their body. Virtually all the elves work against Sauron in the Third Age. But if you look beyond the Lord of the Rings, you'll find that elves did more than their share of dastardly things. Feanor ordered the genocide of an elven subrace because they refused to help him recover the Silmarils, Maeglin betrayed Gondolin, the greatest elvish city, to the forces of Morgoth. What D&D did was they separated the evil elves from the rest of the elves, making them the drow to be easily identifiable.
Am I making sense?