I can only speak about my experiences but it was the perceived need to believe or at least be prepared to believe in a god that turned me away from AA when I first went there for help 10 years ago.
I had a Catholic upbringing and was terrified by priests as a kid. When I became an adult and discovered that it was ok not to believe in god and that terrible things wouldn't happen if I didn't pray and confess my sins a huge weight was removed from my shoulders.
20 years later, I rock up to AA for help with my drinking to be told that I had to try and believe in a god that doesn't exist for me - otherwise there'd be no hope! Despite my grave reservations I tried to keep an open mind to the existence of god and looked into and rejected, like many atheists do, 'alternative' faiths such as Buddhism in an attempt to follow the programme.
I didn't want to 'fake it till I made it' I just wanted to stop drinking!
It's only now, after having resumed drinking for a further 10 years that maturity and experience has shown me that just stopping drinking is not enough. You have to work on all other aspects of yourself, not necessarily to 'fill the gap left by not drinking' but to give yourself the tools , strength and courage to remain sober and develop.
Many folk do just that using religion or other spiritual practices.
Others grow and develop in other ways without the need for a faith.
There is not a one size fits all programme it seems which is not entirely unsurprising.
What does unite everyone here though is a passion for sobriety and through this forum over the last nearly 4 months I've found so much help and wisdom from people from all walks of life, all over the world, those new to sobriety and those with years under their belts.
Although I needed a rational, non religious method to stop drinking and stay stopped I can still learn from those using more traditional AA programmes, and I hope that as time goes by it can be reciprocated.