This seems like a pretty important question– if the prison continues to cause problems for the United States and has almost no benefits (see this post and this post) why hasn’t it been shut down, especially since President Obama has openly supported closing down the prison?
The answer is simple– political opposition. There’s almost no political support for closing down the detention facility (and an incredibly high amount of political opposition) from the Republican party (and from some democrats). That makes closing the detention facility incredibly difficult– Congressional opposition to a presidential action makes it incredibly difficult for the action to occur.
It’s unfortunate– the prison certainly needs to be closed down. But it probably won’t happen anytime soon, especially considering the current Congressional climate.