They (no source) had a pretty unique and fun way of making it fun to do. The reason really was atmosphere and genuine charm in the characters within the game itself along with a shit ton of fun / addicting / SWG-esque community building. (Unlike Destiny which is the most bland fucking game I have ever played)
If I had to guess (no source) Destiny's lackluster effort and lack of audience acceptance after seeing the very drab final product of Destiny made everyone rethink. Unfortunately, Blizzard could make a much more appealing world than Bungie ever could. Anyway, on to project "Overwatch" and we can start the speculation again for another 7 years. I still think they will be pouring effort into smaller games with a greater ROI.