The need for an argument for the complexity of the world to support the rationality argument for belief in God.

In the debate over whether belief in God is rational, why do you need an argument based on the complexity of the world and not the simpler argument that physical existence itself indicates a Creator?
In other words, why not say that the mere fact that I see matter indicates that there is a creator for that matter, or from the opposite direction, argue that rationally, in a world without a creator, there is no possibility of any material existence?
It bothers me that the low entropy argument can only be made after the development and refinement of science and mathematics.