It's just past 8 o'clock on Saturday night. Everyone's watching X Factor, or having a drink, or eating out, or doing something else. Lots of people are browsing around the site at the moment, perhaps they don't see a topic that interests them - why don't you start one?
You're right about the forum being quiet, and I think that apart from the Saturday night effect it may partly be due to the way the site seemed to slow to a crawl for a while. It does often seem to happen at weekends, and Without looking at the server logs I don't have a sensible answer I'm afraid.
I think you have had the decorators in again as today is like watching paint drying. It has taken over 10 minutes to log in and page changes are taking more than 1 minute. I think you have driven people back to their TV's ;-)