The former case makes a lot of sense if the issue is controversial or contentious, but I don't have a good hypothesis for the latter case. My guess is that people found the post useful or amusing but did not see (a) anything they wanted to argue with, or (b) anything they could expand upon. However, I don't have much confidence in this explanation because I am generalizing from one example (myself).
On a related note, I have noticed that making the first comment on a post generally nets you more upvotes than if you made the comment after many others have commented, probably because most people don't read every comment or get tired of upvoting by the time they get to the bottom.
I've known that the mind can be affected by the body's actions, but I often forget this when sitting at my computer chair for long stretches, and when standing and interacting in social situations I've subconciously cultivated a passive, non-confrontational but minimally interactive posture. But simple physical actions can act as a mild nootropic for certain situations.
Article with citations: 10 Simple Postures that Boost Performance
Article summary:
1. Take a powerful pose to feel powerful
2. Tense muscles for willpower
3. Cross arms for persistence
4. Lie down for insight
5. Nap for cognitive performance, vigour and wakefulness
6. Hand gestures for persuasion
7. Gesture to self for comprehension and memory
8. Smile for happiness
9. Mimic to empathize
10. Imitate for comprehension and prediction