Well, maybe the person who created the duplicate thread would like to know that there's already discussions on that particular topic occurring. So if they're wanting to have a conversation about it, rather than re-inventing the wheel of an already ongoing topic, perhaps they might want to join in what's already going on.
And two, they might want to know why their thread then gets virtually no responses because the topic has been played out.
Rather than sitting at an empty table talking to themselves, perhaps the creator of the thread would like to walk over to the table where a whole bunch of people are also discussing it, and join in.....maybe that way they'd even make new friends.
Is it more important to be the creator of the discussion, or a participant? Huh?
And maybe they'll also come to realize that for newsy topics, maybe they'll want to check for next time to see if there's discussions on it.
A thread in a forum can go on for years, and always be fresh, even if a new person quotes something from the very first page of a long threads, and adds their input or insight, without needing to create a whole thread. look at some of the huge threads on here, such as the Mr Beer thread, pr the No Secondary thread, people come in and out of it for years, building upon and contributing to what's already there.