a couple reasons that I can come up with on the top of my head are:
Disney doesn't like bad publicity, whether through official channels or not, and this particular story shows that the people in charge of this project are clearly inept at getting this done and working well with top dogs in Hollywood. So with such a negative rumor running amock through the fanbase, Disney needs to do something about it.
Disney wants to maintain the image that "all is right in WDW" and that there is a clear plan in action. If they are truly planning to announce another idea for HW this week or soon, how does it look if multiple projects have to get redesigned/put on hold in the past 3 years?
Also, there is a stark difference between "Disney is trying to kill this project" and "This project is dying". I don't think Disney is trying to kill this project at all. But I do think they're trying to stiffarm their way through it and complete the entire thing for as cheap as possible. It seems that Disney and Cameron don't see eye to eye on how it should be done, and I don't believe that Cameron can be stiffarmed into concessions. If these two giant powers don't see eye to eye then the project will indeed die.
Iger wants Pandora done...and when a CEO wants something done (even if everyone else around them tells them it's not a good idea) it will take a long time for the CEO to admit defeat on the project.
Disney will never publically acknowledge that the project is in trouble or dead, and if asked directly they will of course say everything is fine. The would rather people just forget so they can put the idea on a shelf in the archives...that is if anything has been drawn up at this point.