Community guidance on comments is clear: comments are ephemeral, intended to live long enough to convey information to either the author of a post, or another person commenting, and no longer. Comments which are conversational are never appropriate, as clearly called out in the flagging UI ("outdated, conversational, or not relevant").
This guidance is reiterated by a current site moderator in What if comments on answers start to grow and look like a forum?, a Q&A posted nine years ago but which appears just as relevant and applicable today as it was when it was first posted.
And yet, when I make an attempt to help improve the site by flagging comments that are no longer needed (and indeed, in most cases should never have been posted in the first place), these flags are often declined. I've let most slide, but the other day an entire group of flags were declined on comments that are egregiously inappropriate and clearly fall into the "No Longer Needed" category. See the comments below How bad is switching derailleur gears under load?, starting with "I have heard that moon is made of cheese and water drips upwards."
Really? A moderator on this site, with the charge to enforce community rules and take action when content violates those rules, made the decision that "I have heard that moon is made of cheese and water drips upwards" not only contributes something constructive, but is such an important contribution that even after the author the post where the comment was posted has read it, the comment needs to remain for posterity?
I am frankly a bit shocked at the latitude moderators on this site take toward preserving comments. The approach taken is drastically different from that I see on other sites in the Stack Exchange network (and of course, especially on Stack Overflow, arguably the model for all other sites). This results in an inordinate amount of clutter under many posts, making it difficult to identify the useful information hidden among all the weeds.
Why were the flags on these comments declined, what value is it that the moderator felt overrides the normal handling of comments, and assuming this is actually an official policy for this particular Stack Exchange site, where is this departure from the otherwise-standard guidelines documented for this site?