The numbers of religions that offer an easy way out for sinners has always been great. If Atheists are merely weak sinners it'd be much easier to join a church that allows forgiveness after some minor act. Paganism can be pretty liberal in what classes as a sin so that would suit most people.

I'm sure there are loads of other reasons out there, ranging from a good way to meet people, which is certainly true, to meeting the right sort of people, historical or cultural significance or even just wanting to make a stand against the other. I'm (A)gnostic but I would support CoE vs all comers as this has helped form my country.

Ah, Bible study groups. I love them. Last one I called god a sadistic psychopath based on forcing Pharoh to refuse the Israelites their request so he could then punish them with plagues. Since it was a group that believed the literal writings of the bible there was no way to "interpret" their way out of that one. My wife didn't let me attend any after that...