Laura Hillenbrand's Seabiscuit: An American Legend is a biographical examination of the life of Seabiscuit, a Thoroughbred racehorse who started as an "underdog" in the racing world and eventually rose to fame and success, serving as inspiration to many of those suffering during The Great Depression.
Although he lost the first seventeen races he participated in, he was trained into winning shape by Tom Smith and paired with a much more suitable jockey, Red Pollard. Under the watchful eye of Smith and skillful riding of Pollard, Seabiscuit went on to win many races, including the Santa Anita Handicap for a prize of $125,000.
All of the eNotes chapter summaries for Seabiscuit (as well as discussions of the book's themes, characters, and critical and analytical essays) can be found at the link provided in the sources tab below.
The eNotes summary of Laura Hillenbrand's Seabiscuit: An American Legend does include all the chapters, as well as the epilogue. The link provided below to that summary clearly includes all 23 chapters. Also attached below is a link to the full text of Hillenbrand's book, a perusal of the Table of Contents for which clearly specifies all 23 chapters by chapter title.
If the purpose of the question is to ascertain why eNotes doesn't provide the full text of the book, the answer could lie in the nation's copyright laws, which preclude the commercial use of someone else's published material without authorization. Also, eNotes does not exist to provide complete texts of books; rather, it provides useful summaries and, when possible, links to online texts, as in this case with the aforementioned link attached below.