Perhaps the standard on HN is that there be a high-quality post and high-quality discussion, and that therefore, it could be that one particular post gets flagkilled, but not another when the community/mods want to discuss an issue but dislike giving eyeballs to a low-quality post.

Or they all get flagkilled regardless of content if the community/mods do not want the issue discussed here, even if a particular post is well-reasoned and well-written.