A book may, and usually does have a title, but it should not have an entitlement.
What I mean is that my first published novel, for example, is titled “Father John VS the Zombies,” but it is not entitled “Father John VS the Zombies.” It is not even entitled to its title, since I granted that title to the book and can change it whenever I please (or even strip it away and publish the book as an untitled work, though that would be pretentious).
The confusion—and why many writers insist on referring to a written work as entitled something—may arise because I, as the author, confer the title onto the book. That is, I entitled my first novel with the title “Father John VS the Zombies.” But once I’ve entitled it, it’s now merely titled that. Clear as mud?