I wonder why, maybe it saves on marketing costs?
I think it's a couple things.
First, I would speculate that it's in reaction to people being upset about certain things in the PAX 2013 demo not making it into the final game. I'm thinking they regret letting phones into that theater. They don't want to set expectations for something they might not be able to deliver.
Second, they just want to see if the strategy works. Does the hype keep building when you announce/advertise early? Or does the hype peak at announcement, implying that's better to announce late? Or maybe the hype just plateaus anyway, justifying cutting the marketing costs.