Shooting comments off into the ether is fine by clicking the page and commenting there. But, if you have a couple of dozen blogs in your RSS feed, and leave a handful of comments a day, clicking back through the specific place to see if you've been responded to is way too much effort. Sites like HN, Reddit, and Facebook, have a central mechanism by which you can be notified.
In the '10s I had a blog with over 1000 readers, I had fewer comments, and less community than the replacement Facebook group has with a fraction of that number.
That may not be a problem for publishers who are purely interested in eyeballs. But that isn't all of them. If the aim is to free content from the walled garden (which I think is an important goal), then it matters.