Greenwald also mentioned that the totality of what Snowden controls is "enough information to cause more damage to the US government in a minute alone than anyone else has ever had in the history of the United States." Let's assume that's not an entirely hyperbolic statement.
From the point of view of the Obama Administration, the real threat is not Snowden's/Greenwald's principled (even patriotic) drip of information, but that an enemy of the US might kill Snowden, and stage it to look like a US op, thus tripping the dead man's switch. Snowden has, on his own, made himself a prime target for any sufficiently ambitious US antagonist.
And so the US wants Snowden back not only to prosecute him, but also to "protect" him. (Nothing like four years of solitary to keep you safe, comrade.)
Until and unless he is granted a pardon or some other form of immunity from prosecution, it seems that Snowden's best interest is to stay in the strongest and most secure country he can find. A country with a highly developed security apparatus (to protect him from hostile agents), one that is adversarial to America (to disallow his rendition or extradition), but not openly antagonistic (to want to kill him to harm the US).
And that is exactly the country where he finds himself right now.
Obama and Putin have quite the chess match coming up. God bless the man whose life is in their hands.
[Edited for clarity]