Retro Studios, best known for their work on the Metroid Prime trilogy, started out as a small, second-party game development company out of Austin, Texas. Due to their success in creating Metroid Prime and Metroid Prime 2: Echoes for the GameCube, Nintendo brought them on as a valuable, first-party developer. Their name eventually became synonymous with their title, Metroid and they continued to make games for the series all the way through Metroid Prime 3: Corruption. Aside from that, they have made a name for themselves by helping to develop other popular titles such as Donkey Kong: Country Returns for the Wii and the recently released Mario Kart 7 for the 3DS.
With so much success, Retro Studios has proven time and time again that they are capable of making great games, so the question that arises is why has Nintendo not given them the opportunity to create a Zelda game?