Why would Iraq's Shiites want to play second fiddle to the Iranians? They're Arabs while the Iranians are Persians. They're sitting on the 3rd largest known oil reserves on Earth. They control the holy sites of Shia Islam, not Iran. And lastly, they have the full backing of the most powerful country on Earth.
Maliki wants us out in a timely manner so that he can consolidate his increased prestige.
He took on Sad in Basra and East Baghdad and won. His standing right now is quite high, and he's feeling his oats. By negotiating a withdraw of US forces and restoring full sovereignty to Iraq, he knows that his position will be secure in the eyes of the Iraqi public. He's a shrewd politician.