He's not classy enough. The Academy Awards are still a Tiffany broadcast, the high-toned classy show of all shows, and when the Academy has gone down the other lets-pull-the-plebes Oscar road (producer Alan Carr and the aborted Bret Rattner/Eddie Murphy shows come to mind) they have regretted it.
Also, Gervais besides being a (brilliant) shock-humor gross-out insult-comedian, is not a movie guy. Look at his credits,TV. He hasn't taken off in movies ("The Invention of Lying" was a flop). The reason why the Oscars have not gone to Emmy and Tony host Neil Patrick Harris is the same. He's a TV guy. I'd love to see them both present, though.
Which brings up my current favorite candidate to host: Ben Stiller. He has a movie in the running ("The Secret Life of Walter Mitty") so he'll have to show up anyway. His presenter stint as a Nav'i was hilarious. He's a smart comedian who's good on his feet and a real movie star.
If Stiller won't do it I'm crossing my fingers that enough time has gone by that Hugh Jackman will have forgotten the pain of hosting, and will be persuaded by returning musically-oriented producers Craig Zadan and Neil Meron to try hosting again. It's like child birth. In time you forget the pain and remember only the good stuff. He was universally praised.