I am published both with publishers and self-published for several months now. The difference in the royalties that I am making is unbelievable. I am making a helluva lot more doing it myself without going through a publisher. At first I thought it was the stories involved. One, being better received than the other, however, when I went to see where one of my novels was placed on the publisher's website, I had trouble finding it. If it's buried, it isn't going to sell. People have to see it. That's a form of impulse buying and it works. Most publishers ascribe to the "what have you done for me lately" school of thought. That means only the new or upcoming books are displayed. If people see it, they can buy it. it's as simple as that. Publishers have to keep their sites fresh and inviting. An author can only do so much.
I have another publisher who makes sure all her books can be seen easily. They move on a continually loop across the screen. She also has them listed in more than one spot. Of course my books sell better with her. I still don't make as much as I do on my own, but at least, she knows how to market and I know she's working her butt off for her authors--all of them--not just the newly published ones.
The point of all this is to be aware of the fact that if your book isn't selling on some publisher's site, it may be the fault of the publisher and not because the book's a stinker. Keep that in mind when it comes time to renew your contract with the publisher.