Fun fact: I've been waiting to post my 200th comment on medium for the past few days because I felt like I'm going to post it for a favorite author of mine and also wanted it to be a good one. Not sure about the good part, but favorite author part, yeah, it's true!
I see commenting as the best part of medium for me, personally. A few things on why I feel so:
1) The joy of seeing someone sharing similar thoughts as yours, except that they have done it in a much bigger fashion or expressed it in a much better fashion. Comments allow me to express those feelings of admiration and inspiration.
2) The joy of reading different perspectives than yours and learning something new. I started out on medium reading about old historical ideas and then branched into several new areas (thankfully not on increasing my subscriber count and that stuff) like your blogs on stoicism, reading about F.I.R.E. movement, reading leadership perspectives, latest technology trends.
3) The joy of seeing someone share their stories on how well they did and how badly they fared. I like reading both because it takes a lot of courage to say I failed and be ready to say in front of a wide audience.