Honestly, why wouldn't they?. They really should be right on top of any new update/game coming out.. pretty slack really.
Even a ~We are working on it~..... just to acknowledge it is known about by them would be a good start.
Why be quiet? Well, it postpones the firestorm for a bit. If they knew the update was coming out later, announcing it would have started the rage that much sooner. Being quiet until the last moment means the blowback begins on Day One, rather than prior to release day.
Personally, I'd prefer the honesty and acknowledgement that it will take a little time to get things here. That may hold off some of the frustration if people are prepped for it. Remaining quiet in this age of instant information doesn't seem to be a solid tactic anymore.