@Majikal:
Because Gaea's Cradle is, in this deck, pretty much the emblematic bad player's favorite card; it is a card that is definitionally only good if you're already in a good position and does nothing, and is a Wasteland-able Forest or worse the rest of the time.
Elves wants it because the deck absolutely needs to play a lot of cards at once and hopefully an Emrakul or a really big Mirror Entity. This deck is, or at least should be, defined primarily by the independent strength of its cards. I mean if you're going to dilute that for Fauna Shaman- Elesh Norn, at least you're getting a very large upgrade in potential power out of it. Tutoring up a Gaea's Cradle so you can go insane with a
Withered Wretch is not in the same neighborhood in terms of risk/reward ratios.