Book subtitles are getting ridiculously long. What is going on?

Blame a one-word culprit: search. Todd Stocke, senior vice president and editorial director at Sourcebooks, said that subtitle length and content have a lot to do with finding readers through online searches. “It used to be that you could solve merchandising communication on the cover by adding a tagline, blurb or bulleted list,” he said. But now, publishers “pack the keywords and search terms into the subtitle field because in theory that’ll help the book surface more easily.”