Why was the question Why do some boarding passes fail to mention when gates close? closed as primarily opinion-based?
I would assume that airlines must have objective reasons to do so, as the few reasons mentioned in the comments of the questions seem to indicate (e.g.: "they don't want to encourage people to turn up right before boarding closes."; "Planes can sometimes leave earlier than scheduled. If boarding is completed ahead of time, they can close the gate ahead of time and leave ahead of time.")