I've noticed this too, Franck.
My guess is because many people on StackExchange still don't value being nice and kind, and prefer to use their power to be negative, overly picky, and hyper-critical.
On some other StackExchange sites (especially Super User), it's common to simply get your good questions closed without any constructive feedback.
Some people just seem to not be interesting in providing others with free carrots. Instead, they take those carrots, and try to use them as sticks.
I've been tempted to set up a question and answer site dedicated to people who choose to only be nice, kind, and helpful. I would be okay if there were only 100 of us using that site, if that happens to be the total sum of people who can see the value of positive reinforcement and kindness.