I think it mostly depends on the number of cars being built now. When I started mine 4 years ago, I think there were more than 10 cars being built at the same time, so it gave a lot of activity on the forum, both with build threads, and problems/questions/answers. How many car are being build now? Perhaps not even the half of what it was at that time, so this should explain the lack of activity on the forum.
Even if my car is finished now, I read the new posts every day, and try to help whenever I can (when I don't raise a problem I'm having myself.. still
). But more and more built are MX5 based now, and I wish I could help more, but I can't because I have a Sierra based Roadster experience (and perhaps many members from the "completed-car club" feel the same?). So we are in a transition period between these 2 concepts, and this might be another factor.
Just my humble opinion