The back matter in the Image issues of Casanova served as a sort of journal for Fraction to record the personal aspects of creating the story. In one issue in particular, he delved into some pretty intense family stuff. Some few readers responded in a really shitty way, but at the time he said it made him rethink trying to connect with his audience so personally. My guess is that the original back matter is not being reprinted to avoid any more of the below-the-belt nonsense that went on the first time.
Of course, it may also just be to preserve the uniqueness of those first editions. They really don't add anything to the story, so I wouldn't worry about it.