Reason: Probability. Since God is faith, and faith is belief without evidence, that means any and all doctrines are equally probable. It is just as probable that a hamster in a top hat is ruling the universe as is God or Allah. Since any story is likely, that means there is an infinite number of possible stories, all equally likely.
One divided by infinity, well, is not actually a number. So the probability of God existing in any definable way is absolute zero. Obviously, this does not mean that A god does not exist, just one that, even if it does, we can never approach any reasonably close understanding of it. So why bother?