Opening the attractions over a full year goes against all prior actions in theme parks and is bad business sense. Look at the Diagon Alley event: hotels and attractions were lined up for a large media event gala. Same for the Millennium Celebration, 100 YoM, and more. Same reason why you'll see Kong, Sapphire Falls, and whatever is in CityWalk open around the same time. "This is what we have new open, now."