I think what happens is someone new joins the forum and then just starts reading and posts a few comments just to get started not realizing they should check the dates of when the thread started. It is nice to recall some of what has been discussed before.

When I sign in I just go to the link that says new posts and it just brings up anything new that has been posted since I was on the board the last time and I start working my way through them. For sure more likely to comment on the items that come up first and as my time gets tight do more reading than commenting. But then as long as someone else comments that thread will be in my list later anyways.