The company claims that the book has trade secrets.

Among other things, Apple is known for very zealously guarding its secrets. And when a former employee of the Cupertian giant wrote and released a book called App Store Confidential, the company’s reaction was quite expected.
To begin with, we note that the author of the book is Tom Sadowski, who until November last year ran the App Store business in Germany. That is, this is a very informed person who had access to the information that ordinary Apple employees, and especially users, do not know about.
Sadowski’s book came out in Germany only yesterday, and Apple immediately sent a letter to both the author and its publisher, demanding the cessation of sales of the book and the recall of all copies with subsequent destruction. Apple explains its demand by the presence in the book of commercial secrets of economic value, and the author, according to the company, violated the terms of the employment contract.
Sadowski himself claims that he did not reveal any secrets in his book. In addition, reporters who had already managed to read the book also did not find any insiders there.
How the story ends is still unclear, but with a high degree of probability Apple will sue.