So, I have an answer that maybe most people haven’t considered.
It’s not so much Quora, but the Internet in general. I think atheists tend to flock to the Internet because they’re looking for a sense of community that is lost when you reject religion. So many times when I was an atheist, and heard other atheists express, that they wish there was a ‘church’ for atheism.
Online social communities fill the void left by church.