It sounds to me like Maliki didn't really try. This article says that in 2008 the Iraqi Parliament ok'd this US Military's immunity but in 2011 it would not have been possible, why? Is it because Maliki is not behind the US?
Again, if Obama was any kind of a leader, he'd have negotiated a better exit strategy for the US. He'd have put it onto Maliki's shoulders to persuade Iraq's parliament to pass the immunity legislation.
Also, the article even admits that this is not the case in every country. The article clearly states "These protections, which are common in nearly every country where U.S. forces operate, were guaranteed under the 2008 status of forces agreement negotiated by the Bush administration; Obama simply demanded that they continue under any follow-on accord."
Um so ok. That's room for the US Forces to stay. Period. And again, if BO was any kind of diplomatic leader, he'd have a way to make this possible in Iraq too.