For me, the original posters must not be held at fault, and the way I see it, no one is blaming the original poster here for opening a new thread. They’re new, so they really don’t know anything about how this place functions.
It’s rather about misguiding these original posters. If we already know that a topic is duplicate, guide them to a more popular thread with (almost) the same answers. After all, they open topics with the intention to get answers. It’s a different story if someone is opening a thread to become popular on their first day. We had such a case a few months back if anyone remembers(the man who complained about subs in every other thread?)
Just as Lutra said, merging topics breaks the flow, then why create these flows in duplicate topics in the first place? Let the original poster know about already existing threads and continue the conversation there.
If the same answers are found in the same duplicate threads, useful information gets buried down. I hope, in the future, if someone asks a duplicate question, rather than creating a flow in that duplicate topic, we can continue the conversation in an already existing thread.