I think a lot of it had to do with not having time. Rebooting the game and starting fresh leving yourself only 16 months is not anywhere near enough time for a game like this. The 3 studios that work on CoD have 3 years to create each new game and CoD is just a PvP game. When you look at Destiny on what D1 actually had. There was no why Bungie had time even with the 2 other studios working with them to put all that kind of work into D2 in 16 months. Especially knowing their rebuilt engine takes 8 hours just to put out content before they can edit it.