The author bought 11 paper books because they wanted to make money posting a meta-review of the literature analyzing the arguments from all of them together. Wh

The author bought 11 paper books because they wanted to make money posting a meta-review of the literature analyzing the arguments from all of them together. While they probably understood the points after a single book, they would have lacked the complete coverage (and the marketing hook). I would expect someone writing that to have read the 11 most popular books.