Well, the whole park being a shell is kind of true, the park still works anyway.
As for why the park is a shell is kind of interesting. It also coincides with why islands of adventure is really good. For those who don't know, here it is. (them park tourist is my source)
Animal kingdom would have a number of key differences when it opened, but the animal attractions were costing more and more, to the point where these were changed.
The first would be a symbol of the park, the animal carousel. It would be three tiered, one dumbo style bit, one normal carousel and one carousel on water. The tree was chosen instead. http://www.themeparktourist.com/features/20131125/15135/unbuilt-disney-animal-carousel-disneys-animal-kingdom
The more interesting one was originally going to be in the site of primeval whirl, and triceratop spin. Called the excavator, it was going to be the thrill ride of the park, similar in thrill to big thunder mountain. Thanks to coast, this wasn't built and the site was used for the midway games and rides in around 2001. More details: http://www.themeparktourist.com/features/20131201/15216/unbuilt-disney-excavator-disneys-animal-kingdom
However the big thing was beastly kingdom. It would have featured a number of major rides and would have been in the area avatar is going. This would take a while to write so read here for details. http://www.themeparktourist.com/features/20131017/14745/avatar-what-was-beastly-kingdom
The interesting thing is that when this was canned the imagineers left, and worked on island of adventure instead.
The result is a park that is still kind of empty. So why hasn't something happened sooner? Because I, along with many others still love the park. The limited attractions are some of the best in WDW and the attractions take a while to ride. They are some major crowd pleasers.