Because 'faith' is not a pathway to truth. Faith is the excuse given when there is a lack of evidence. If faith is your only reason to believe, then you cannot distinguish between Hinduism / Catholic / Muslim / Rastafarian / Satanism / Wicca / Christian / Judaism. All promise to have the 'real' truth, with divine inspiration & knowledge, yet none provide any means to prove the existence of their deity.

By its very meaning, faith is the excuse given when one does not have a viable explanation, reason, or proof to support one's belief. Why do we rely on reason and logic before believing in every other part of life... yet, when it comes to the ultimate truth, THE most important matter of our lives, humans suspend rational thought and choose 'faith'? ( <--- indirect quote from The Atheist Experience)

To what end would people choose to take things on faith? Likely due to their place of birth (or familial beliefs), with no regard to analytical thinking. Conversely, 'faith' is not a factor in NOT believing in something. The vast majority of atheists have actually given thought to religion's being non-rational, and then deciding against faith. This clearly indicates the decision is not faith-based, but instead relies on research and evidence (well, the lack thereof) ;)