You and I might think of our miniscule Voting Power being used to help upvote content we like and mostly we just ignore content that we don't like. In this mindset, we typically will not downvote very much because our downvotes have very little effect. However, I think for the whales, they see downvoting as a way to control the reward pool. If they think a post is getting too much reward relative to its quality then they might downvote it.
There is also the phenomena of hate-flagging people too. It's sometimes hard to separate the what is hate-flagging and what is somebody saying that a post is low-quality. Promoting bad products and low quality images are perhaps reasons somebody might downvote.
I've seen downvotes for tag abuse - where a community "owns" a tag and then downvotes people who don't follow that community's standards for quality.
shrugs When it comes to this particular poster though, he is controversial, so some people are going to have a lower threshold before they down vote.