Another point to consider is that if he sits on the fence or vacillates before making announcement, it makes it easier to pinpoint the sources of any leaks that do occur. If I tell Bob that I'm contemplating trading for Boldin, but I tell Jim that I'm leaning toward Pace instead, and the next day the papers are reporting that I'm looking into Pace, I can move quickly to snuff out the leak.
It's all about compartmentalization of information. At this stage of the game, no GM really knows what he's going to do anyway, so any information he gives his staff is essentially of equal value (worthless).