Why is it that when someone perceives some -illusory- purpose in the design of the universe...?

...why is it that when someone perceives certain signs of design in the universe, they directly presume the creator/designer must have been the Biblical god? Where is the logical connection between the virtual design and Jehovah? Even if the universe was designed, why does it always follow from it that it was God? Why not the Flying Spaghetti Monster, Zeus, the 3 Cosmical Stooges or it's all just an experiment run by some crazy duck scientists in the spaceship?