That's a totally different question 
Why we don't believe in God is (usually) because there is absolutely no evidence indicating such a being exists, no logical necessity for such a being and no requirement that we conclude upon the questions such as "why is there something rather than nothing?". Every argument for his existence is a failure, riddled with fallacies or relying on stupid shit like Plantingas "true basic" belief idea. Essentially our epistemological standards are far too high to accept any of their reasons as sufficient to believe.
Christians assume that they are justified in their conclusion to these questions, they are fooling themselves by believing that these answers are available, and being arrogant by claiming that they are the ones with the answers.
Oh, and you don't have to quote me verbatim if my response is too harsh for them. I'm not the one who's having the discussion with them so frankly I have no reason to be polite about it.

Why we don't believe in God is (usually) because there is absolutely no evidence indicating such a being exists, no logical necessity for such a being and no requirement that we conclude upon the questions such as "why is there something rather than nothing?". Every argument for his existence is a failure, riddled with fallacies or relying on stupid shit like Plantingas "true basic" belief idea. Essentially our epistemological standards are far too high to accept any of their reasons as sufficient to believe.
Christians assume that they are justified in their conclusion to these questions, they are fooling themselves by believing that these answers are available, and being arrogant by claiming that they are the ones with the answers.
Oh, and you don't have to quote me verbatim if my response is too harsh for them. I'm not the one who's having the discussion with them so frankly I have no reason to be polite about it.
.