It would appear the high-flying discourse of r/atheism failed to live up to the exacting intellectual standards of reddit:
We know many of you will wonder what happened to /r/politics and /r/atheism and why they were removed from the default set. We could give you a canned corporate answer or a diplomatic answer that is carefully crafted for the situation. But since this is reddit, we’re going to try things a bit differently and give you the real answer: they just weren’t up to snuff.
I know I’m shocked, as I’ve so often been impressed by the arguments presented by r/atheists.