Closing a question as a duplicate because there is already a question with similar wording (but assuming an entirely different tech stack, architecture, coding style, and goal) is a frequent enough experience that it became shorthand for the site's problems.

There was kind of a fatal mis-match between the questions being asked and the intended kind of questions that were being answered. The actual asks were often incomplete diagnostics of the questioner's current problem, frequently focusing on the wrong thing (because if you don't have the full knowledge of the thing you're going to be prone to incorrect assumptions of the diagnosis). SO's intent, though, was a more mathematical "here's the question, here's the programming concept that explains it" so you get the best explanation of how a linked list works under a completely unrelated problem. Which is fine, but the site's culture and design only partially acknowledged the disconnect.

The whole site developed a reputation of being something approximating the reverse of the comments under recipes that substitute lard for cream and wonder why their cake tastes funny. Lots of questions of "How do I implement this functionality in Y? We can't change our tech stack because of other factors, so it has to be Y" questions answered by "If you just use Z instead you wouldn't have these problems" and "closed as a duplicate of this question for how to implement the non-Y version" when there was a perfectly fine way to do it in Y.

In my experience, the problem wasn't the user base, it was the moderators. I would be getting useful answers (or questions) from the users, when out of the blue the moderators would shut my question down for some reason. I once complained to the management (literally), explaining why I thought the moderator was wrong, and got my question restored. But that was too much like work.