We're back
I've found that with many of the groups I moderate, that many, many members/new members join and probably visit the gallery, see what they want to see and then they don't participate in any discussions. Also ... many people join this site, take a look around and join groups and then leave and never return. I have dozens of members in those groups I moderate that haven't logged in, in over a year!
As the topics increase, so will the numbers but I'm of the opinion that there are a core number of members that always keep a site going and that is far, far less than the numbers of "members" many of these sites state they have. It's a numbers game with the more numbers of members for a site, they more marketable the site is IF the owners want to try and sell it. I think it's a way to boost the site's worth but far too often, these sites are kept going by the couple hundred members that actually do contribute.