I read a few pages of the sample, and I agree that you should be looking at your writing before looking for external factors.
In the pages that I read, you have awkward word repetition ("as if" two sentences in a row), an uncertain voice for one of the characters, ("I feared you wouldn't know me" sounds formal, "Hound-dog business been good to you!" sounds - well, I'm not sure what, but certainly not formal), a lot of back story (before I care about the characters enough to want it), odd, hard-to-understand phrases ("the scandal of Great-granddad's remembrance"), and unclearly attributed dialogue ("You find out yet what a bullet can do to a man's head?" and on).
I know you didn't ask for a critique, but you're rejecting the obvious answer to your question based on the belief that your writing is at at four or five star level, and I really don't think it is. I'm not saying it's not a good story, or that the first few pages are an accurate representation of the book as a whole, but there are a LOT of books out there, and if your first few pages aren't dynamite - I think that might be why you're not getting the downloads you hope for.