It follows because God is defined (by theologians - and they're the ones who get to do the defining) as a being outside the created universe. If you define God as part of the universe, you are defining a being that theologians do not recognize as God. Evidence of its nonexistence is of no significance.

Taking the metaphor of God being to the universe as an author is to a book, redefining the book as including its author does such violence to both the concepts of "book" and "author" as to render their study meaningless.