I suspect many just spend their free time in other places. brian, for instance, has been active on StackOverflow a lot. Others have taken to blogging for interacting with the community in the way that they might have done with Meditations posts previously.
Personally, I stopped visiting regularly several years ago. The site was terminally slow (seems better now, so +1 to that). I wasn't learning as much as I used to answering people's questions, and answering for the sake of XP wasn't doing much for me other than being a big time sink. I had fewer questions of my own and the nature of those were sufficiently esoteric that I was more often going direct to places like #p5p or #toolchain on IRC.
So, mostly, I think I just outgrew it.
It looks like most of my posts since 2009 have just been 'community announcment' type posts. I only checked in today because I got an email with a bug report referencing a thread there.
Kudos to those saints who are still here, participating vigorously for the next generation.