My point is I don't think curators primarily curate for rewards. Because the rewards are much lower than the work involved. At best, the rewards are a bonus for whatever primary reason that curators vote for posts.

I do not disagree here but I think, still the rewards gives something back to them which makes them happy, otherwise, they would have just powered down and leave this place, if they are not regular content creators. And definitely if the improved curation quality will result more rewards, then we would see more manual curators, which is also a good thing for content creators.