I think the thoughts around comments are dead-on. That is, it seems that when a piece has comments, that inspires comments - readers spend more time reading/responding/engaging. It's a bit of a vicious circle, I suppose. But, if you write a comment-worthy piece, you'll generate those comments which will begat more comments - which increases time spent reading the piece/engaging with it. Thus, more earnings. That makes at least some sense to me, even if it is frustrating.