Ask HN: Why don't HN'rs respond to threads?

There are a LOT of unanswered questions posed to commenters on HN. Why don't more HN readers click on the threads link to read what people are saying to them? If you don't, why not?

I know there have been discussions of having notifications, but more than most forums, commenters here are pretty smart about how to best engage online.

When there is a civil request for expansion on a comment, I nearly always find replies from parent commenters to be helpful and enlightening. But it's much more common that the original commenter never responds.