Why should textbooks be free.

Since I've started studying, I noticed something really strange, textbooks and science books are surprisingly expensive.

Some books that I would consider essential for an engineering undergrad, like Oppenheim and Willsky's book on Signals and Systems go well above 150 USD. I've even seen biological sciences books go for way more than that.

Furthermore, is unlikely you will ever use Oppenheim's book for the whole length of an undergraduate course, and unless you start doing research in that area, it is very likely you will never touch that book again in your entire life. There are always the possibility to rent the book, which goes for about 99 USD in Amazon.

Scientific books are thought to be expensive because there is a whole deal of research behind them, there are tons of money invested so the book can be written and a professor (who is already being paid) has to devote some time to write it. There is a proofreading process (which sometimes is done by undergrad students also being paid already)

Economically speaking, it just does not make any sense, the US government most likely is paying many of the grad students, postdocs and professors that are writing the book via grant money. The professor may or may not get an advance on the book, and the royalties he will get on the book are around 10% of the cost of the book. Which means that both Oppenheim and Willsky should get around 15 bucks for every book that is sold. 

Also, is not like scientific books can earn you big bucks, mandatory books like S&S may get you good money, but most likely you won't see a lot of royalty money, especially for highly topical books in advance graduate courses.

Then the next question is: Why charge for it, originally it made sense, since printing was the only way to communicate new ideas and teach scientific ideas, and printing is overall an expensive process. However, the internet brought that down, if you are living in the internet age, and you are writing a book because you want to educate people, there is no good reason you cannot give your book for free. With 10% of royalties you are clearly not getting rich, and we can distribute a thousand copies with the click of a mouse.

You can always publish it, and expect someone will buy it in print (I know I still do sometimes), but I do believe is a researcher's duty to allow people to access freely to the contents of the book.

Why? For one, the money to develop the knowledge that you use to write the book is most likely taxpayers' money. The money given to you so you have a hefty team of undergrads, grads and postdocs probably is also taxpayers money. And the fact that you have students going out of their way to write a book, might actually hurt them in their pursue of a graduate degree.

And finally, I do believe that as educator, the ultimate goal of the professor should be to pursue the education of as much people as they can reach. If their objective is to make money, they are probably in the wrong business anyway. The main question I like to make is: Do you care that people pay for your book, or do you care that people read your book? If the answer is the former, you probably do not care the IEEE and other printing houses charge 20 bucks for an 8 page article.

Luckily I'm not alone on this, and many great Machine Learning professors have made their books freely available in the internet. I do believe there is a possibility to get a great ML education based only on free books, although some of the best books are still not available for free download.