It’s the upvoting. It pushes agreeable “sounds good” opinions to the top, short-circuiting critical thinking. Notes and tweets don’t have that. You have counts but comments are not ranked by counts aside from the parent note (trending). 

And since those places are communities, people naturally have the need to belong and are more likely to align themselves with the popular (most upvoted) opinions rather than risk losing reputation for independent takes. 

The nature of notes going by makes it easier to forget discussions and move on - more forgiving on the user. 

My totally unscientific 2 sats