Also, the minimal design, and the lack of an algorithm targeting my personal preferences with the express intention of tricking me into reading more stories makes a huge difference.

I really enjoyed commuting by bike, to the point I would go to certain places solely for the bike ride, and leave within a few minutes. I was also addicted to smoking. HN is like my bike addiction, while FB and Twitter feel more like my smoking addiction.

That's a good analogy. Yes, HN is from an era before the social engineering began.