I can recall in my early steemit days when my comments were earning MORE than my actual posts.
And that makes sense.
To start, when we are new, we are not known so our posts are floating around unattached. They do not get any views. However, by commenting, we are relying on the author's following.
Also, we usually do not attract people with much SP when we first start. In the comment section, you find all kinds of SP there. It helps to be where the heavy hitters are.