Yet, there's one tiny tiny possibility that I have considered for why he hasn't. Before becoming president, you make promises, have goals, and overall think you know what you're going to do on day one.
However, after inauguration you go for your first big debriefing with the CIA, FBI, etc... The things you learn there completely change the course what you want to do, or can do. You find that we were constantly in significantly more danger than any citizen could have anticipated.
Now, I don't find this to be likely, but just something I've considered. Why in the world would have Obama gone from wanting to close Gitmo, to being pretty much against it? Politics alone don't seem to cover it, since pretty much everyone wants it closed. Logistics? It doesn't seem that hard...