On one hand, it's more about promotion and name recognition. Day has a mega-serious-promo-machine behind her. Anne Rice is, simply put, Anne Rice and has huge cross-genre appeal. Jennifer Kacey is well-known, but not at the level of Day and Rice. Rankings have nothing to do with how well written or well plotted a story is. If that's all it took, we'd all be millionaires, right?! And I doubt the rankings have anything to do with the setting, either. Day and Rice and a handful of other authors are just in a league of their own for so many reasons and one really can't compare other authors to them. That said, I also see that "Together in Cyn" is an Ellora's Cave book. I am not going to get in too deep about the recent history of Ellora's Cave -- there are plenty of blog posts plus the #notchilled hashtag on Twitter where you can read all about what is going on with EC in the event you are unaware of any of it. Back in Sept 2014, EC sued a blogger for defamation. After that, the entire romance reading and writing community decided to boycott all EC books. Later, some EC authors begged readers to not buy their EC books because they wanted their rights back based on low sales. Jennifer Kacey is one of those authors who has requested readers not buy her EC books -- in fact she has requested readers not buy "Together in Cyn" (see her website http://www.jenniferkacey.com/booklist.html). So in this very particular case Jennifer Kacey wants her ranking to be low so she can get her rights back to her book and republish it. So, there are a plethora of reasons why a book may or may not be selling well.