I throw a few fg on the 6th act being on heaven, the text telling that Tyrael failed to suppress evil even with the destruction of the world stone, how it spreads even more, Tyrael becoming a fallen angel (last line), and how a shard of Diablo soulstone was retrieved by Adria (that used it on Leah).
Probably angels getting pissed at Tyrael contacting the mortals and how the ws being destroyed, have affected the balance, while he gets banned, we need to restore all that.