There are way too many people spamming comments with bots, and they are so easy to spot, they don't upvote, their comments are all generic, and you see them popping up on other peoples posts. Really annoying.
They do work when people autovote their comments though, which is part of the problem. Go read @marketreport's comment section whenever he posts. He must run an autovoter and now everyone autocomments him, like he'll have 70 comments in under 5 minutes, all spam