the pages begin double in size, piled and then folded in half, with the middle stitched together to form the book. Or something lilke that. So the last end pages and the first opening title and publishing pages are from the same sheet of paper.
maybe it's for notes...
They are called "endpapers" and are to protect the first and last printed pages from the wear and tear of being immediately adjacent to the covers.
It is like the part of a running track beyond the finish line, so that quick readers don't come to an abrupt halt