I like to read the comments on leadership books listed on amazon. I find recurring themes on the comments.
Complaining that the book contains nothing new. - My suggestion being the leadership books contain nothing new because there are grounding principals regarding leadership that each of the authors recognizes and are in their own way pointing those principals out. The answers are there many readers just do not want to accept the principals and are possibly not ready for leadership.
Complaining that the author does not give them exact answers for every problem that arises. - There is no shortcut every book read should be expanding the knowledge base of solutions to problems that arise. The answers being sought are cumulative by reading and understanding numerous books.
Complaining that the contents of the book are over-simplistic. - The actual concepts of leadership are basic and it is up to to the reader to find their own method of implementation.
Complaining about a lack of supporting data. - Some concepts in life do not live in the world of empirical data. A fact of life
It is obvious that many readers are not really reading to learn but are reading with an I know better mentality.