Knowing that the Dawnshards carry Commands, and that the Shards carry intent, I think that the reason a lot of the Shards have trouble acting is because they are Intent lacking Command (looking at you Harmony)
I think Odium somehow was able to wield the Dawnshard Change, and used it to splinter the other Shards
I think that Honor was somehow able to take the Dawnshard away from Odium (perhaps dying in the process). Stripped of the Command to Change, Odium has been bound to the Rosharan system
Many have noted how similar the effects of the Dawnshard are to awakening. Its also been noted that Endowment seems to have some sort of plan against Odium. I think Endowment is creating a new Dawnshard, perhaps with a sufficient amount of Breath. It seems within the Intent of Endowment to Endow someone with a new Command.