Why? The proposition is that existence and non-existence may be human categories that do not apply to God. We have no trouble realising that questions such as "what colour is God?" or "where does God live?" may reflect misunderstanding. How can we be sure that the question "does God exist?" doesn't reflect a similar confusion?
"That sounds stupid to me", doesn't constitute an argument.
We don't expect a dog to understand calculus. Is there any good reason to expect that humans should be able to grasp the divine? Or to put it another way, if human reason is unable to construct a satisfying conception of God, does that in itself prove that God is unviable? Or does it tell us about the limitations of human rationality?