I'm writing a report on this book for my AP World History class, this is one of the questions I have to answer. Can anyone that has read the book spit ball ideas out to me?
Chapter 13 starts off with an excellent example to support the answer given in #2. The discovery of the famous Phaistos Disk and the way that it represented a form of writing that was not adopted indicates that writing only developed and was taken up when there was a perceived need for it to be adopted widely. As the chapter explores, many different factors feed in to the invention of writing, in particular the bureaucratic need to record.
One reason why writing didn't get invented in some societies (and didn't spread to them from other societies) is that those societies did not have any need for it. Diamond talks about how writing is really only useful if you have a pretty complex society that is based on agriculture and has a pretty organized government. Societies like this need writing for record keeping. But other societies that don't have bureaucracies and such have very little use for writing so they would not be likely to invent it or even to borrow it.
What is interesting about writing is that it developed in separate independent parts of the world. Yes, it became important as civilizations grew to develop a system of keeping records - first symbols and then individual characters. What are interesting are those civilizations with great bureaucracies and wide-spread that did not develop writing, such as the Inca.