And if someone is in an accident during that brief window of time you are in a theater it isn't likely to make much difference in the scheme of things. What could you do in 2 hours that would have made a difference? Emergency services via 911 could make a difference within that time, but you could not.
You obviously do not have children. There are certain rules in place (mainly to prevent the hospital from being successfully sued) that make it so a hospital does not operate on a minor without at least one parent's permission. In the event that they need to do surgery to save the child's life, they will do it without the need of the permission. But if the surgery is instead to save an arm or a leg or something like that which isn't life threatening, they will wait to get the parent permission. If the surgery is time sensitive and the arm will be lost if the two hours that go by mean the difference between the child keeping his arm or losing it, I'd rather not find out after the movie that if I had known during the movie, I could have saved my son's arm.
Extreme situation, but children get injured all the time and without the parents' permission, time sensitive procedures would never get done.