So I was dredging up old posts and flagging superfluous comments that are mainly gratitude as "no longer needed". I have raised about 20-30 flags today. While most of them have been marked helpful, several recent reviews declined some of my flags. The interesting thing is at least one of my declined flags' corresponding post has been removed, which should prove my flags are helpful :). Some other declined flags point to comments along the lines of "Thank you." "That's very helpful." "Your answer helps learners like me." I don't see any reason they should stay. I won't link those comments. I believe mods can see my flagging history.
I understand it is a cultural thing that some users feel compelled to thank their answerers, and I appreciate that. But I recall reading this: https://ell.stackexchange.com/help/someone-answers