I believe part of the thinking was: the leaker will be found eventually, who do you want to start the story about the leaker? If some government agency were to unveil Snowden's identity they could cast him in whatever light they chose from the very first image (who looks like a defender of freedom in a mugshot?)

Look what happened to Bradley Manning, the first public image of him was his chat confession and a huge amount of deeply personal details that really had nothing to do with the leak.