I'm curious as to why this Message Board was created, how it works, and why no one uses it, as far as I can see, for communication between members regarding paddling trips, stuff for sale, questions, etc.

Its like a lot of boards for other groups... they are withering on the vine, so to speak. I think its a shift in how folks interact. Facebook, meetup, and others all tend to be more 'mobile friendly' and support instant messaging.