Not many people are buying "Piggyback to the End of the World" as an e-book. It even comes free with the trade paperback, but no one seems terribly interested in even the free copy.
Why do you suppose that is? Sure, everyone likes a real book. I do too. I also like being able to carry a whole shelf of books in my pocket.
So, where are you, mysterious people who like a good e-book? How do I find you?