The plain Wood Armor is made to be the worst armor in the game and there's one thing I like about how bad it is. Wood Greaves have a whopping 0 Defense and, unlike the Amethyst Robe, it has no bonus. The Greaves also needs more wood than the Wood Helmet, so the cheapest piece of the set isn't the worst! Wood Greaves aren't entirely useless though because you need it for the Set Bonus of +1 Defense.
(Arguably, the Djinn's Curse is worse than Wood Greaves because it gives slow fall, which makes it more than just Vanity but is way worse than anything you can get in that point in the game except Pearlwood Greaves, but it's clearly made for Vanity.)