The person best qualified to assess the relevance of any previous answers is often the OP. Far too often, the already-existing answer is years old and either no longer the best answer, or doesn't actually address a major part of the question. Or it simply was never a very good answer to begin with.

What would be the harm in pointing out previous answers but leaving the question open to further contributions? If the previous answer really is adequate, it won't attract further responses. If it's not, well, now its shortcomings can be addressed.

Closing duplicates makes as much sense as aggressive deletionism on Wikipedia. It generally means that somebody missed their true calling on an HOA board somewhere.

I will say that I had questions erroneously closed as duplicates several times, but I always understood this as an honest mistake. I can see how the asker could find that frustrating and might feel attacked... but that's just normal friction of human interaction.