The big problem: All comments have a half-life of half a day at most, and even during that short time they are buried in a mountain of other comments. If a story is popular (many potential readers that I could reach) there will also be hundreds of comments, mostly low quality, that make finding good ones hard. If there only a few comments so a good one will stand out more there won't be many readers.
Writing a blog post has a much higher chance to be found over a larger period of time. Probably, depending on the blog. A choice between getting attention (by borrowing the fame of reddit or HN to draw in readers) for a very short period of time, or be easier to find over longer periods but then it depends on the fame of your own blog.
So it is not worth spending a lot of time and effort trying my best because I only reach a handful of people in the first place, but even if it's hundreds, they are all just story- and comment browsing randomly for their daily does of entertainment. That means whatever I write will be forgotten pretty quickly because in the end it's not all that important. Nobody reading any of these comments actually needs them, no matter how much wisdom is in there.
What I mean by that is that only when you actually end up using what you read in a practical way does it really matter and you remember. Everything else, even if it's really great wisdom, if you have no practical application for it in our own life your brain does not put any priority on retaining the content. Even apart from comments, I for example took loads of courses (edX, Coursera) outside my own field, at the time I spent a lot of effort and even became a community TA in some of those courses (chemistry, statistics, biology). However, I forgot soooo much by now, because in the end none of it has any practical implications for me. With some completely random (all kinds of topics!) comments, even when they are good, it's much worse.
Therefore I don't expect such comment sites to ever rise above what we have now. It just does not really matter for either readers or writers. The quality will always just be "good enough" (on the low side).
PS: Oh and by the way, in my long reddit and HN experience, what gives the most "Likes" rarely is the quality technical stuff - but rare personal anecdotes.