The location of the page numbers in a book is a matter of design choice by the book's publisher. There are several different ways that page numbers can be presented in a book, and each design choice has different advantages and disadvantages.
One popular design choice is to place the page number on the outer edge of each page, either in the upper or lower corner. This makes it easy for the reader to quickly find the current page number, as it is always located in the same place. Additionally, having the page number on the outside edge can make it easier to flip to a specific page in the book, as the reader can quickly skim through the edges of the pages.
However, some publishers choose to place the page number on the inner corner of each page, particularly in books that have a lot of margin space. This design choice can be aesthetically pleasing, as it keeps the outer edges of the page clean and uncluttered. Additionally, placing the page number on the inner corner can sometimes make it easier to read the text, as the numbers are not in the reader's direct line of sight.
There are some potential drawbacks to placing the page number on the inner corner of the page. For example, readers who are not familiar with this design choice may have difficulty finding the page number at first. Additionally, if the book has a particularly tight binding, the inner corners may be difficult to read without having to bend the book open significantly.
Overall, the placement of page numbers in a book is a small but essential design choice that can impact the user experience. The decision to place the numbers on the outer or inner corners will depend on a variety of factors, including the book's overall design aesthetic and the intended audience. Ultimately, the goal is to create a book that is easy and enjoyable to read, so readers can focus on the content rather than the design.