The only time studios refuse to pre-screen films to critics is when they know they have a potential bomb on their hands and they want to rush it into the theaters to try and recoup some of their production costs before reviews tear it to shreds.
In this case it's a ridiculous $300 million dollars!! Seriously? They spent $300 mil on this thing? For that amount, the characters better come right off the screen and dance in the aisles.