It's easy to blame things on the nameless, faceless "Disney" and ignore the fact that the people who work there are actually human beings. What I suspect happened is this:
The folks at the Disney Event Group sold a premium event at 9:00 PM. Being well after the park is scheduled to close and not a normal time where your first thought would be that people are eating dinner, they never put 2 and 2 together. The Disney Event people are not the same as the Food and Beverage people, meaning there's no one person who said "haha I'm going to screw the plebes." Two different groups stepped on each other's toes and created a scheduling conflict.
I'm not saying it's okay, but I think it's probably a case of different departments working in silos with poor communication rather than deliberate disregard for the "regular" guests.