My main guess: people feel that commenting "this is good" is redundant to an upvote. Why use 14 words -- including puffery like "worthy of anyone's reading eyes regardless of generation" -- when you've already expressed your recommendation through a one-click upvote?
Or possibly: Since there's no article downvote, the easiest way to express a strong opinion that the article is awful is to downvote comments praising it as 'great'.
In lieu of sparking up conversation about an article I think is good, because it may be regarded as "redundant", I'll just vote up and keep any opinions quiet.
Or possibly: Since there's no article downvote, the easiest way to express a strong opinion that the article is awful is to downvote comments praising it as 'great'.