From our comment privilege help page, comments are not for answering the question:
When shouldn't I comment?
Comments are not recommended for any of the following:
- Answering a question or providing an alternate solution to an existing answer; instead, post an actual answer (or edit to expand an existing one);
As it suggests, you're meant to instead submit an answer. Answers actually have our full rigorous quality assurance process applied, comments have almost no QA at all: we can't edit them if they need correction/improvement, we can't downvote low quality comments, we cannot cast delete votes or flag them for review queues, they don't bump the question to draw critical attention by reviewers who might vote or take action on it, and so on.
I've encountered some comments like this one which are just an answer in comments, and also redundant because there's an actual answer available. I've flagged these for moderator attention with the reason "answer in comments, delete" or something like that. The recent occasions have been declined. (I would flag such comments even if there wasn't an answer to make it redundant, since whoever wrote it should have submitted an answer instead for proper peer review.)
Why are these flags being declined instead of the comments being deleted?
I request they actually get deleted, as a matter of site quality maintenance. I don't expect the mods to hunt them down around the site, but if someone (anyone) takes the trouble of flagging them for mod attention, I'd prefer the mods delete them rather than leave them lying around.