Why was Adonalsium destroyed/split?

[Cosmosis]

I've been reading about Adonalsium and I've seen a lot of theories or facts about how he/it was destroyed and who did it and stuff like that. But I haven't seen or read anything about why he/it was destroyed. Maybe there just isn't enough evidence to have a discussion about it and the topic has been abandoned to the dark recesses of the 17th Shard. However, I think the "why" of its destruction was more important that the "how". 

A simple explanation could be that the 17 who destroyed it just wanted the power, but I feel like this isn't the right answer. I'd like to hear your ideas or knowledge of why he/it was destroyed.

On the Coppermind Wiki it just says "For unknown reasons at least some of the 16 who shattered Adonalsium did so believing it was the final option left to them, suggesting its power may have been targeted as a last ditch attempt at self-preservation." so maybe you could just give your theories as to why he/it was destroyed. Looking forward to your answers and theories! 

[DeTess]

We know that the destruction of Adonalsium was done by a group with very different ideals and personalities. Such a group is generally brought together by necessity, so I suspect that something forced their hand with regards to Adonlasium's destruction.

We don't know if Adonalsium was actually a benevolent god. He could have been ambivalent to his creations, or even a jerk or a tyrant. Therefore, the group might have set out to destroy Adonalsium, and then found out that they had to take up the power or else someone else would (or Adonalsium might reform).

Alternatively, some kind of existential threat had turned up that Adonalsium refused to fight, so those that took his power did so to do what he had refused to do. Maybe Adonalsium had fallen asleep and those that took his power did so because waking him was found to be impossible.

[Weltall]

According to Khriss, the participants all had their own reasons for doing it. That some of them were apparently motivated by the belief that it was 'the only good option left' is suggestive but doesn't really narrow the options down much. Adonalsium could have been doing something that the future Vessels saw as actively dangerous, he/it could have been uncaring but not malevolent and they felt this needed to change, it could have been that Adonalsium was for some reason no longer using its power at all... too many possibilities and no real way at this point to say what's more likely than not.

An interesting possibility comes from the story that Ym tells in Words of Radiance, about One who knew all but experienced nothing, so it became many, in order to experience all things before eventually reforming when something called the 'Seventh Land' is attained. This could be a distorted recollection of Adonalsium and has parallels to certain strains of thought in theology. Adonalsium might have desired to be shattered for some reason and the Vessels helped the process along, whether knowingly or not.

Another possible avenue for theorizing has to do with fainlife. It's described in the sample chapters Brandon has released from the Liar of Partinel draft and while that's not canon and everything in it is subject to change, Brandon has made references to it several times so we know that the concept itself is still canonical (for example he mentions that Yolen has 'two competing ecologies') even if the form might not be identical to the old sample chapters.. The concept finally appeared in a published work in Arcanum Unbounded when Khriss compares Scadrial to Yolen in the essay on the former system. By implication from some things Brandon has told us, fainlife isn't the dominant threat of the Dragonsteel sequence (part of why he started writing Liar of Partinel was to show a time when it was a major threat, since Dragonsteel Prime glossed over it) but it's still around so it could be part of the reason for the Shattering. Or not, at this point Brandon only knows.

It's highly unlikely we'll get much in the way of substantial information until Brandon writes Dragonsteel when the full story will come out. We may get some tantalizing hints along the way but he's gotta save some surprises for the books themselves.