Commenting is indeed important. I comment on blog posts for various reasons. These are the primary ones:
Support great content. I love to see people writing quality posts that stimulate ideas and conversation, provide some kind of education or entertainment, or give us all something of beauty, such as wonderful artwork or photography. I want to reward people who are producing great content. (Oh, and by contrast, I ignore bad content!)
Create community. One of the most wonderful and unexpected things that has come out of my involvement on Steemit is friendships. I did not embark on this journey to make friends and get involved in community. I actually came here to find my voice as a writer, and I loved the idea that I could also make a little money for my writing along the way. But by far the greatest reward has been friendships and community. I do have quite a few contacts I've made through Discord, but some of my friends and acquaintances are people I know purely through conversations here on Steemit. I love love love it.
Live the golden rule. Everyone knows this rule: Do to others as you would have them do to you. In other words, we are all in this together, and we need to treat others with caring and respect, and reward their good efforts. If we expect to be treated with kindness and respect ourselves, we most certainly must treat others in kind. Usually the kindness will circle back to us.
I'm honestly not sure how much financial reward there is in commenting. I have never taken the time to calculate it. But I'm hoping that at the very least I'm making some karma bank along the way! :-)