Strategy of books or of applications or Operating system which are available freely online are often confusing. What is the point of giving these things freely when they can be charged?
Often we see some books which are available online. They have the printed copies for sale in a bookstore near your home. But still they are available in readable pdf versions online. Wondered why this happens? Do you think that the publisher of these books do not have copyright to take down these free online versions?
Or, we see the Operating system (Windows) or the programs (Microsoft office) available in pirated versions online. Don't the giant Microsoft have enough power to take down these websites?
In fact they do have the power to take down these pirated versions. But their aim is different. They are not looking for the money which this program, or Operating system or the book is going to give them. They want the users to be comfortable or addicted to Windows, Microsoft office etc.. They want to make sure that due to high cost of the products, people are not deprived of using their product. Their long term goal is to make the people addicted to their product and when the people have enough money, they go and buy the good version.
The authors also want book to be readily available to readers so that they can have more fame than money. A highly priced book will lead to no one reading the book and appreciating the talent of the author. But if it is available freely online, many will read and the skill and fame of the author will be establishing globally.