There is great comfort in the predictable, especially before bed or when other things in life are changing.
2. TO GAIN BETTER UNDERSTANDING OF THE TEXT
At some point many readers must realise that there are far too many books in the world to continue reading the same ones over and over (although I do know middle-aged Tolkien enthusiasts who read Lord Of The Rings every single year). But children who ask for the same story over and over are often getting more out of it each time. This experience is especially valuable with adult input during some of the readings. Story book apps with auto-narration are especially useful in this process, because adults have a smaller tolerance for repetition than their children.