Nah, I don't think there's so much fear of content living forever.
People tend to comment mostly on big accounts for visibility and potential rewards. And then their feed, starting with their friends first, most likely, if they have them on notification.
Yes, I do believe we are a more post-oriented platform than Reddit, so reading the posts to engage to takes time. And if you also count in writing your own post, well, time flies by. And there's probably something else you have to do every day, so... maybe tomorrow you'll comment more...
Ah, let's not forget Discord, steem.chat, and github (for those who follow the repositories there). Each simple task takes time.