The underlying system has some weird behaviours and moderators are sometimes compelled to mark flags they find helpful as unhelpful. This might happen, for example, if you report something as "rude or abusive" where they agree that the content should be removed, but disagree that the user should be penalized. But also, a lot of problems are better handled by just editing out objectionable content. When you flag a question as a duplicate or as "needs improvement", that goes to the community; but everything else is sent to a team of 24 volunteers overlooking a site that still receives thousands of questions a week and is still full of years-old comments that should be cleaned up but which nobody has gotten around to yet.