I'd be interested to hear the answer to that from someone who has read the contract in full and understands it. I personally haven't had the opportunity to do so; I'm only going based on other members' interpretations.
Because, put simply, if I want to so much as add a fence to my backyard, I have to get approvals from my city, the HOA and the CDD. That's my property, and I should be able to do it if I wish. If I were Disney, though, at least according to the interpretations and posts of other members recently, I would be able to put up that fence without asking anyone, or if I did have to ask, they'd be contractually obligated to say yes.
Why should Disney, Universal, or whatever other large organization be able to circumvent government processes that individual/personal landowners have to deal with?
ETA: A 5th gate would have major impacts on the infrastructure beyond the district's boundaries, so they should absolutely have to go through extensive review with the counties and the state.