The book doesn't seem to contain any information about historical figures like Dnyaneshwar Maharaj, even though he is quoted. Why would the text exclude the life stories of other important spiritual leaders?

The preface in Chapter 0 establishes a clear purpose for the text that explains this focus. While it quotes Dnyaneshwar Maharaj to support the principle of serving a Guru, the book's primary goal is not to be a collection of biographies. Chapter 0 distinguishes between different forms of service: writing about 'extraordinary jurists, historians... and writers' is worldly service with limited fruit, and even writing about 'many saints' is described as potentially 'one-sided.' The author asserts that the 'best and most certain service' for salvation is to write and study the biography of one's own Sadguru. The Shri Sai Satcharita is an embodiment of that ultimate service, and its focus is therefore intentionally narrow to facilitate deep, unwavering devotion as the path to spiritual liberation.