The explanation I've heard for these is it's a low-effort bot comment that builds activity on the commenting account.
Whether that actually increases the value of an account or not, I'm not sure. But it's enough that spammers seem to think that having comments & replies on an account.
It may also be purchased comments to improve "engagement" metrics on videos for the creator.
My favorite ones are the comment threads for sentimental songs from the 80’s—you just get a flood of heartbreaking stories from older folks talking about their first loves, now passed on.
It's not just me / the music videos I look up then, is it? I can't help but wonder if it's some kind of YT hive mind, bots, or Google's own algorithms pushing those comments to the top.
First part of your comment is right, but your reasoning is wrong. A couple years ago, YouTube changed the visibility of negative comments, such that positive comments are prioritized (can’t like a comment if you don’t even see it).
This was also around the time they removed the thumbs up/down count.
This was to prevent creator burnout; imagine if every video you put out had some snarky diss against you in the comments.
I'm not convinced that the current trend of positivity is not caused by bots, but I wouldn't be surprised if the old system was just based on engagement. Meaning that upvotes and downvotes would both push the comment up. This is not intuitive, but would fit with what we've been seeing for the last decade or so.