Comments were the primary source of engagements before all these voting bots, as that time, people were expecting to get upvotes from others, if they are engaged. But with these voting bots, I think, there is very less value for comments from engagement perspective. Most are busy with making a post and then buy upvotes.
However there is now a new form of rewards for comments. If you observer, @steemhunt or @musing now rewards comments on a regular basis. I am sure, more such platforms will also evolve. So if one is not interested to buy votes, then they can still earn a little by having meaningful comments / answers.
I am sure, if we kill all these voting bots, comments will again take a peak.