I think the biggest reason isn’t even the evolutionary root, but people’s tendency to chime in when they disagree, whereas they MAY hit the like button if they agree.

I would even say the number of comments shows how controversial something is while the amount of likes shows how uncontroversial it is.

Comments take more effort than hitting a like. You want to add your 2c and before you know it, others want to address what you said, too. And you get endless repetitions of the same arguments buried deep in chats and threads.

Finally, there is nothing more addictive and compelling than the notification “Someone just replied to your comment”