We're told by knowledgeable insiders the reason Warner Bros. picked Snyder for Man of Steel is that the script by David Goyer was rushed, is still a bit of a mess, and that Warner Bros. needs someone who won't spend months or even years trying to get it just right (i.e., Aronofsky), because time is the one thing they don't have: The studio must have a new Superman movie in production by 2011 or they'll be subject to potential lawsuits by the heirs of the superhero's creators.
We're told that Snyder was not really Warner's first choice to direct Superman, but that a director needed to be hired imminently. Privately, even Snyder has confided to agency sources that the current Superman script needs work, but clearly Warner Bros. believes he can get it done faster than Aronofsky.