Why are you an atheist?

A few weeks ago, I stumbled across the blog site of an atheist, Atheism And The City.  The individual who runs this blog, and posts under the name pseudonym "The Thinker", is a prolific writer.  His (I assume the writer is male) site has five or better posts per month, 69 so far this year, and over 700 posts since the blog's inception in 2009.