I often reach assumed duplicates via Google but still get very insightful answers. If I click on the link pointing towards the assumed original, it's sometimes completely deserted with a single two-line answer that's been outdated for three years.

And they're happy to leave the duplicate up for the inbound google benefits it provides.

And then the duplicate doesn't even have the answers you need.

The best part is when the duplicate is related to your question, but the duplicate question is structured differently so you don't know how to apply its answers to your question. Sure, if you already knew the answer the duplicate answers make sense, but without that knowledge (hence why you asked in the first place) they are completely unhelpful.

If the duplicate doesn't answer your question, you're supposed to edit your own question to indicate why the linked question wasn't helpful. At that point you're supposed to magically attract enough attention to get the question reopened. Unfortunately it rarely works out that way.