Welcome to MobileRead, chicagofilms!
One important detail that you're leaving out is
where you bought the book -- that may have some bearing on the situation and perhaps options.
However, from what you're describing, I'd say the most likely answer as to why is that the book was made with forced half inch margins.
If you're in a Sony Bookstore book, you don't have much in the way of options. If you're in something else, you
may be able to convert it, depending on what it is.