Money, why would any player invest another 10 years of their life to destiny? The higher ups know this. No point in making D3 when the current one works. Not to mention the devs would have to make a brand new bash of content including armor and weapons. Bungie is restricted when it gets to creativity and everything cost money, not to mention licenses and copyright issues. If bungie was to make a D3, it would take a considerable effort for the community to come together and ask for it. Player count would gave to skyrocket for the higher ups to even consider it. Thats just not something I see happening