This is a pretty common question and should probably be in the FAQ.
If you search the archives, you can see plenty of people asking this and a few third-party sites that will notify you of comments.
Last year, dang posted this:
> I look at it this way: it's designed for engaged, prolonged discussion if and only if people continue to be interested enough in it to remember. If they aren't, activation energy falls below a certain threshold and attention naturally moves on to something else. That seems healthy for curious conversation, which fits the prime directive of HN (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...).
> What we don't do is resort to technical tricks to keep that energy buzzed up. We're optimizing for curiosity, not engagement.
https://news.ycombinator.com/item?id=27897211#27901918
