Because people lost interest in posting
And the posts that you see are 'way way back', are like that because we do not delete them(or do it rarely)
Guess the first reason is the forum itself. Like Wolfyx said, there are a lot of topics to delete, you can't find what you need.
Discussions are also slow because I would not choose to post a problem regarding anything on the forum - Undernet has good help channels or at least 20 people I know that can provide help about everything.