The nature of a soft opening is that it's the "beta testing" period for the ride (or show), and as such the ride can be opened and closed as needed by the imagineers and operations CM's to tweak or fix things. And very importantly, Disney doesn't want to create any expectations that the ride will be available before the official advertised opening date. After the official opening you're free to go to Guest Relations and complain and want your money back if the new whiz-bang attraction is closed for the whole day, but during the soft opening period you can't do that.