Each starry aura only gives a limited number of fragments (either 1000 or 2000 depending on series) and they are evenly divided between all the divines in the series. On completion, you only get 100-125 fragments for each divine of the series the starry aura is for. You would need multiple of the same series star horses or fragments from other promos, luck bmi and/or Ascent of Olympus to actually get the divines.