Length is 100% marketing. There is no commercial market for 15-20 page essays, which would be the ideal length for a lot of business books. (The famous Harvard Business Review cases are typically this long.)

The reason many business books feel fluffy is that these 15-20 pages of solid content are spread over 300 pages to meet the expectations of readers and booksellers.

You forgot the first 2 chapters whose purpose is to lay out with anecdotes how everybody does it wrong because they don't follow that one insight and argue that anyone who criticizes the book has the wrong mindset for being a successful entrepreneur.

The same formula seems to be common to all the "popular X" genres (science, psychology, etc), and has been for years. The Selfish Gene followed it. So do Malcolm Gladwell's books - the last one of his I read, I had to restrain myself from throwing at the nearest wall in frustration at his nonsense.