Simply because of pacing. Honestly I would have rated this higher if some of the fluffy language was taken out, the overly academic language was simplified more, and if the book was about 75-100 pages shorter. 
The content was captivating at most points. I got confused when some dramatizations were included, simply because I didn’t see the need for them. 
I would recommend this book, just keep in mind that it’s not going to be fully exciting the whole way throughout.