Is it because there are so many threads with hundreds of pages of posts?
I'm also a regular on Techkings and they recently had to close some of the more popular threads and start new ones with the same or similar name.
They said one of the reasons was because the site was sending 'new post' emails to all subscribed users whenever there was a new post in a big thread.
Could it be that is because users are automatically 'watching' any thread that they post in rather than having to subscribe manually.
Just my two penn'orth, I don't really know much about websites tbh.