This is because photo shoots are brilliantly done in order to maximize the positive features of the models. The lighting, the makeup, the clothes, the angles and the sheer number of photos taken will ensure that there are some good photos. Also, in most cases, the photographers have plenty of experiences in capturing great photos. And of course in the last decade or so then the process of airbrushing has enabled any not so good bits to be removed and make the photos even better.