A number of convincing reasons have been advanced, however I heard the book was researched and written by a 'sister' in London Bethel. An attractive young sister who, before going into Bethel, used to work as a research assistant at the British Museum.
And I don't think sisters are allowed to write any material that is used for 'teaching,' whether WT study articles or book study publications
After all, everybody -- well, every holy high roller, anyway -- knows that holy spirit doesn't flow through those of the feminine gender. Especially attractive young ones.
Which does rather beg the question, why the heck did they publish it in the first place ... ?