Attention and User Acceptance Data
Links flow easily across blogs, so Google may eventually judge that portion of the web looking for other signs of quality that require more commitment than a quick mention. As they get better at determining real from fake they can surface the best few blogs and submerge the rest, all while displaying more content from other verticals, like books.
Ranking at about #120 in the search results I just saw a book about a topic I did a link bait for. It was freely available online and over 300 pages in length. Luckily my link bait is more aesthetically pleasing, modern, and was linked to from major newspapers. If I launched the same link bait a year or two later that book probably would have beat me. I am not sure if I would have been able to buy enough exposure to override Google’s desire to make the organic results overtly informational and from editorially trusted sources.