Well for someone who wrote a book about it, you sure do not know how marketing works. Your views are not the problem it is the book; This looks so cliche that many other "developers" wrote in the same fashion. The book has public domain images with the book cover program I seen in many other books. The file is PDF instead of an actual working file for known book devices like amazon or B&N.
Your design in book does not even look like a book but rather something you liked from a computer. No way to know how much words you have put. Very common title like you didn't put effort on the title. On the topic of effort the sections are so common in other "game development 101" books it might look like you stole it from an article. Lastly, your book vs free articles about game development startups is what makes people not want to buy it. A quick google can help people find the same article with the same title and the same section from the book.
Do you even know anything about books, you you even have rights to use unity logo on commercial book sales, etc. The marketer you spend $600 wasn't bad at his job it was your book that fail. Sorry if i'm being harsh but you really have not made any reason for people to buy your book.