A lot of amusement and theme parks regularly open at 10:00 AM and do just fine. Cedar Point, for example.
I don't know why Orlando has conditioned everyone to think opening at 9:00 AM is a requirement. If you're a morning person, fine. If you're not, earlier openings just make your vacation that much more stressful.
Also, yes, it's a money and maintenance thing. If corporate is giving them the option of either: A - opening at 9:00 AM to be "in line" with the other parks but closing early so people barely get to see the park at night, or B: opening later so people can see more of the park at night, I am very glad they have apparently chosen the second option.
That said, June-August in Florida mean it basically doesn't get dark until 9:00, so still having 9:00 be the standard closing time isn't late enough.
Nobody tell him about the unannounced 5th portal - Muppet Metropolis.