My 2 cents is that attrition happens at a higher rate than new members join. The fact of the matter is that the boards are a tad hostile to new members. Whereas facebook for example is a bit more friendly to new members. Furthermore, facebook transactions are not as regulated as the boards. Here sales are broken down between copper/modern, gold/silver/bronze and mixed. It's just too overwhelming for new members. Why not have a single sales subforum?
Also, agreeing with other people that have commented, most people here are interested in sales. There are basically 0 discussions on the modern, copper, gold subforums that are not related to prices and what is hot. This is especially glaring on the modern subforum where one would expect discussion on current books.