You're definitely onto something. I think the difference here is that comments can actually mean something for both people involved.

If I genuinely get some value out of what you post and try to offer my take on things then it's likely you might get some value out of what I post and we'll be more aware of eachother in the future. Thats something that isnt a factor on facebook, it incentivizes people to actually leave genuine comments.

If you do actually connect on some level, you can use your steem power to vote to see more of it. It's a very different game to normal social media. Maybe I'm just optimistic, but I think that small tweak makes all the difference.