A theory of everything must include a theory of God, presuming He exists. And a theory of God must explain why God is. It is not sufficient to demonstrate the credibility of His existence, as we have done in the lemma "Does God exist?". For a theory with a credible account as to why God exists - a hypothesis - is vastly more credible than a theory that merely conjectures that there must be a reason that He exists - a gap.
Mainstream Christianity has no explanation as to how God came to exist. Instead, it postulates that God has always existed. Supposing this to be the case, we are still left without an explanation as to how the transformation from absolute nothingness to a universe in which God has always existed took place. This need not be a transformation which took place in time, but it is still a transformation.
QO, on the other hand, has a perfectly natural account for how God came to exist, as we have discussed in the lemma "Does God exist?". This explanation is clearly to be preferred.