Not everyone values marginalia, said Paul Ruxin, a member of the Caxton Club. “If you think about the traditional view that the book is only about the text,” he said, “then this is kind of foolish, I suppose.”
A book can't only be about the text, it has to be about the reader's interaction with it and thoughts about it. Without these, the object has no value.
Annotations are the traces left behind of how one valued a book as they read and interacted with it.