I would guess HN guidelines-ishness. Plus, the well-off don't like discussing sex, money, religion (spiritual or favorite programming language) or politics online, and that hits two buckets. I would wager that the average HN reader is far from poor, although may have been in the past. Better to seem to stick our heads in the sand than have real conversations if doing so benefits us, because it fulfills the objectives of the site. This doesn't preclude enthusiastic discussions elsewhere.

It is difficult to get a man to understand something, when his salary depends on his not understanding it.

- Upton Sinclair