Because your attempts at preserving God's eternal pre-existence is made at the price of denying Jesus' divinity by insisting that "the holy thing" that was born was a mere man.
Wrong! "What" was born was God united with humanity, but still the pre-existing God. Or do you deny that Mary gave birth to God?
In your attemnpts to make sense of a divine paradox in our eyes, what comes out of the protestant side is denying Christ's divinity and over-emphasizing Christ's humanity. Typical Age of Reason error.
Show me where I made that insistence. Post please. Show me where I said that Mary gave birth to a mere man.