They are what we call the photoshoot geniuses. Natural born models! When it comes to the professional photoshoots, there's such thing as A-cuts and B-cuts. A-cuts are the photos that will be used officially and B-cuts are normally released beforehand or even afterward, as the "behind" photos. They are normally the unedited versions and few candid pictures too.
Now, some of the top celebrities are the VIP of these photoshoots because of how they make even the B-cuts flawless and high quality! It maybe from the years of experiences but I do think that their natural charismatic instinct and beauty helps them out in front of the cameras.