Interesting find, thanks for sharing. As to the question, I am an atheist for basically the same reason an object at rest (relative to its frame of reference) stays where it is until an outside force acts on it. It is the default position and so far there has been no compelling reason for me to consider changing that. More simply, the theist hypothesis has fallen far, far short of meeting its burden of proof.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'