I've been thinking about the higher age group of this site and I think I got it figured out a bit. Being an atheist isn't as uncommon in the younger generations. And generally more accepted. Therefore they have no "need" to find a site like this. A lot that do come here, came as most do, as a possible dating site. It doesn't really function in that way and they leave.
I came to this site attracted by the name, agnostic.com, but never as a dating site; I don’t care to date in person for good reasons, let alone online. I’m a 59 y/o European transplant (it’s much easier to be agnostic or atheist over there) and find difficult to come by the non-religious type where I live, in VA. I belong to several active social groups in which the religion subject (along with politics) is avoided as a rule, although there’s often a conservative someone who will insert it in conversations. So, I find it very refreshing to come to this site and be able to discuss anything -even religion- in an intelligent way without having to fend any Bible thumpers.