An interesting peek behind the curtain! I had no idea publishers go through so many cover options before settling on one. In marketing, we normally only provide 2-3 options for creative to clients (but often brainstorm more). But now I think about it, it makes sense. If it's in print, it's out there for years. Marketing creative has a short shelf-life in comparison and if it doesn't perform we can modify it next time around (or if it's digital, simply swap it out). Publishers don't have that luxury.
Yes, I found it interesting too. If you know about a book, fine- you buy it. But I'm sure there are many people who, like me, just look around, it is then I believe, that it is the cover that actually sells the book. So if the cover doesn't attract my eye, it doesn't get picked-up. And this is it, what does attract my eye? Very often it depends on what I'm looking for. If I'm looking for fun, then anything lighthearted or cartoonish will make me pick it up. If I want romance, well I'd probably look for a heart, or something and so on... What would put me off is something confusing, fuzzy. Prominent lettering would make me look and so would a bold, unusual image... nothing, bland or wishy-washy. But that's just me, my taste. That's why when I was commissioned to write a history of Rajasthan since I worked for an architect who restored a Royal Palace there, and I also had to design the cover I chose a majestic drawing from the architect to show what it was about and as the title "RAJPUT" (Son of a King) actually summarised who it was about, I placed it at the top of the book in big red letters, then as I was a "no-one" placed my name at the bottom of the book, in the same colour so there would be a balance and not a contrast but in much smaller dimensions. That's something else to bear in mind. Is the author more important than the title or vice-versa? They cannot be the same size- one must predominate, if you don't want to cause a kind of blur in people's eye- and the same goes for the imagery. But as I said, that's just what I think.