Don't know what to say
In terms of animation, that was awesome. Sounds are well done, and visuals are appealing. We'll never really know what happened, will we? Tragedies like this happen, and sometimes we don't even know why. This is only my opinion, about to be as flawed as anyone else's, but I'll say it anyway.
Could be they didn't see the point in life as a whole; that there really was no reason to exist. The whole "God" thing they brought up, maybe they just couldn't see what they should've believed in. But, like I said, we'll never know. Not anymore, at least. The only thing we can really do is hope for a better tomorrow, as cliche as that sounds.