This is a big question for me too! Especially since they didn't seem to have any major reason to burn a lot of cash or to run out of money! Was it maybe a lawsuit, fraud or regulatory issue? I would LOVE to know.
I think the real threat is going to be more of a side-effect of AI. The fact that the current models may produce results that we can't foresee; therefore, a sufficiently advanced AI is powerful AND unpredictable, hence uncontrollable.