When you are looking for a book on a subject, it is important to understand the difference between what is on offer at Amazon and by Google.
The content of Google books was created by scanning the contents of multiple libraries. These books were scanned, characters were recognised and the spelling was checked. The resulting product is significant because this collection is based on the buying decisions of the libraries that were processed in this way.
Amazon is an auction site. People sell books and if you do not know what you are looking for, you may end up paying good money for extracts of Wikipedia. This may be disappointing but it is perfectly legal.
When you buy on Amazon, you get a dead wood item. When you get a book from Google, you get a digital file. When you buy from Amazon, you have to consider the cost of shipping and the time involved. A Google book is send over the net and it is almost instantly available.
As Google does scan books from libraries, they effectively provide a solution to cover the inadequacy of the publishing industry. This approach ensures that books will remain available even when they are no longer in print and consequently no longer commercially viable.
PS I wonder if they have specialised libraries like the one held by the Tropenmuseum.