Ask HN: Why no filter for exact dupes?

Why doesn't HN have a filter against exact dupes, posted hours apart? It seems like an obvious feature.

Like this:

https://news.ycombinator.com/item?id=26205064

There are going to be false negatives due to semantically exact dupes that are not exactly the same URL. Even the same URL can be spelled differently; e.g. trailing backslash or not, domain redirects, URL encoding.

Still, it seems worth having some sort of similarity function which at least warns the user with an extra prompt.