Answer:
This would be done to present the topic of the book to the reader
Step-by-step explanation:
The general reason for the use of a prologue or an introduction in any work of art is to present the topic of the book to the reader.
The theme of the book even if it is non fiction would be specific as it is in most of the books so it is better for the reader to have some idea of what they are going to get inside the book from the outset.
This only has to set their expectations in the broadest sense of it and not rally give away much about anything in the actual narrative