The public does indeed get what the public wants, which to some extent is what the public is told it wants. This is why the public is in the state it's in. .
This.
And it's not just books. People like to think that they have independent will, and while a person does, people don't. It's a pack mentality, which is why some incredibly stupid things all of a sudden become popular - dayglo trainers, shellsuits, twilight, mullets - they become fashionable items because the powers that be say they are the in thing, and so everyone suddenly wants one, regardless.
Marketing is a complex beast, but a huge amount of it is convincing people that they need or want what you have, and if you have good marketing, you can get people to want anything.