This comment was deleted/moved to chat, yet it seems to me that this particular comments meets the requirement for posting comments: it constructively suggested an improvement to the answer, especially since "add comment" is now "suggest improvements" (the other comments, not so much; I agree they should be removed.)
I know that "comments are supposed to ephemeral", but that alone doesn't strike me as a good reason to delete useful content. If the content is useful, then it is useful. Simply chucking it in the bin seems ... counter-productive, at best.
This is not a new phenomenon on this site; I find that on all Stack Exchange sites I've contributed to, comments get deleted on this site significantly faster than anywhere else, even compared to some other more subjective sites that tend to generate a high number of off-topic comments (e.g. Politics or Skeptics).
I appreciate that the moderators have to clean a lot of off-topic bickering, but I really wish they would take a bit more care in not throwing out the baby with the bathwater. Personally, I am always very careful with content that users create in their spare time. Not every comment is typed as a stream of consciousness, and sometimes writing even a comparatively small comment can be preceded by some amount of research or thought.
I'd hate to see that destroyed if it's a constructive suggestion for improvement, which this comment was (technically, you could argue it's still there in chat, but no one reads that, so it's effectively just deleted).