Sometimes it's for a better picture (looking up from under lowered eyebrows, for instance), and sometimes it's just how their faces look - consider the phenomen

Sometimes it's for a better picture (looking up from under lowered eyebrows, for instance), and sometimes it's just how their faces look - consider the phenomenon of "resting b*&^! face". Many people do consider a neutral face to be aggressive or unpleasant, studies show, regardless of the intent of the person with the face.