I work at Priceonomics, so maybe I can shed light on our motivations.
We make the kind of content we love and we sell products so that we can afford to make more of that content. The two products we actually sell (data crawling for companies and books for people) aren't particularly well-suited toward SEO (though our original idea, a Price Guide which we killed years ago, was).
Anyhow, we're a content site that's trying to get by without using ads. I think most of our regular readers appreciate we're trying to pay the bills by selling things instead using ads. We'd like to avoid jamming our site with advertising if that's possible.
Using a web search engine is asking for rankings based on web structure, not rankings based on product quality.
You might think it's bad to take advantage of that, but refraining from doing so doesn't likely yield a fair product quality ranking, just some different unfair rating.
I kind of feel used when I see them pop up.