All of the reasons given in the article are plausible - higher cost, right after Fourth of July holiday, and the recent California earthquakes - but, I think it has more to do with the cost. Disney recently jacked up the prices on their already expensive tickets. They are quite simply making it unaffordable for a whole lot of families to go there. I suppose Disney is relying on possibly attracting more foreign visitors who they think they can gouge.
The essential American soul is hard, isolate, stoic, and a killer. It has never yet melted. ~ D.H. Lawrence