Someone once said: "An atheist can't find God for the same reason a thief can't find a policeman". I think that pretty well describes the primary cause for atheism. Of course, spiritual ignorance would be a close second.

Ditto what physics said.  Why don't you tell your god next time you pray to him to come pay us atheists a visit?  He should know right where we're at, right?  That should end all doubt instantly.  No more theives--er, atheists!

Also, I would contend that you are the spiritually ignorant one.  You can not imagine a worldview outside of that painted by your narrow religion, and you are supremely and grossly ignorant with regards to the thinking, background, and motivations of atheists.  Many atheists I know are quite spiritual.  Spiritual is a state of mind, and requires no belief in the supernatural.  One does not need a creator god to feel awe when gazing at the heavens.