When I'm reading articles I often check with HN for reactions and discussion. This works best for recent articles. Old articles (like https://news.ycombinator.com/item?id=8874499) don't allow commenting anymore. Where do you discuss those?
As new articles get on average very few comments don't expect people discussing old comments. Perhaps you can reformulate the content in a new setting and gain attention. With 10 million post in HN is no wonder millions are sleeping for ever.
If you want to say something about an article, writing a blog post is a way to spark further discussion. If it's interesting, it will spark a discussion on sites like Reddit, etc.