Louis XXIV
Le Roi Soleil
Because the game is still in Alpha. Most info they could give about the game wouldn't be set in stone.
Anyways, if they did give all the info at once, that would kinda be boring. They want to keep us on our toes, excited, trying to get the next little drop all the way until they release the game.
Pretty much both reasons sum it up. I know one company that was praising a new feature for a long time. Then when they released the game, it wasn't there. It turned out to be more complicated than they were expecting and they didn't have time to complete it before the game was released (there was some issue with the game being rushed about by the publisher as well, which probably contributed to this feature being dropped). They admitted that it had been a mistake to mention this feature before they were sure they would put it in because it got people's hopes up for no reason. (EDIT: I wasn't talking about Peter Molyneux, but that's a good example).
As far as the info drop. I do think they need to add something more to keep our interest going, but they also want the big reveal at E3, so it's hard to find a balance. I believe Civ4 had one amazing IGN article where all the Civs were revealed and it blew me away how much info they were willing to give out. But, then again, it turned out the game had so much more to offer that they had actually held plenty back.
I'm hoping a similar thing will happen here, but we've got a long way to go.