Once a certain quantity of comments is reached, hardly anyone new to the conversation will read all the comments before commenting. If the purpose of commenting is to have one’s comment read, then it doesn’t make sense to contribute to already-long discussions.
I tend to avoid commenting on heavily-commented posts, because those usually feature well-worn positions without much chance of substantive contributions making much difference, and are usually dominated by a fairly small clique of frequent commenters (this isn’t directed at CT specifically, but it does happen here; I’m a member of the ingroup at some blogs myself, so I see it happening from both sides) who are focused on their ingroup interactions and don’t pay that much attention to comments from outsiders (unless they are flamingly provocative).
This is one of those posts that invites everyone to share their experience without really adding up to a conversation. There's sort of a discussion going on but, as I expected, nobody's addressed my point at all. Eventually, if it goes the way CT discussions often do, someone will make more or less the same point, but ignore the fact that I've made it already.
Update: The comments morphed into a discussion of "comment bait" -- what topics inspire the most comments. My contribution to that was
Declare the “END OF” something. Books, teaching, good television, bad doctors, an era, and epoch, a school of thought, a social pattern, a word, a meme, etc.