What if that's the point, though? I like the theory that Adonalsium allowed the shattering to happen. What if he realized a being like himself, full of contradictions, could not create a varied enough universe? Maybe he allowed the group of 16 use the Dawnshards to shatter him and take up the shards, and told them as a condition they must spread to different worlds (a condition some of them obviously ignored). I don't know how someone besides Ado could have used a Dawnshard without his allowance considering it takes the power of a deity to wield them. And as far as we know the beings that shattered him were not deities at the time of the shattering.
What if the "different" Dawnshard (per WoB) was Hoid? Ado secretly gave him a Command to make sure his postmortem will was enacted, so now Hoid wanders the universe to ensure worlds with multiple shards are kept safe.
I'm newer to the cosmere so if there's a WoB that contradicts anything I've said let me know.