I can understand why they might want to say much about this show right now.
Looking at recent history:
Their last attraction opening was poorly received.
The last large night show to open in an Orlando theme park was a disaster. (Rivers of Light)
If they know that this show isn't going to be the best thing ever, there isn't much reason to hype it given that it's going to be whatever it's going to be, which may not be great, and it's not something that's going to drive vacation bookings anyway.
I think they have little to lose by waiting until they know things are working and on time, and then sharing details a couple of weeks before opening to get locals excited and coming to visit.