I've seen that before, and I've never understood it. All the more odd is that it's often exhibited by the same people who are quick to say "we're already had a thread on this" when someone starts a new thread on a topic that's been discussed before.
It's almost like they think that a particular topic, once it peters out, is "supposed" to be closed forever; a new thread on a previously-discussed should be ignored in favor of referencing the older one, but said older one should only be reviewed rather than revived.
That's patently absurd, of course, since new posters who hadn't joined before or missed the thread the first time around might just notice the topic now and want to discuss it. For that matter, some of the older posters might want to offer a new thought or insight. That's to say nothing of the fact that a policy of discouraging discussion tends to be anathema to the whole point of having a forum in the first place.