Didn't write because they didn't know how. In the Western Hemisphere before Columbus, not only could they not read and write, they were not familiar with the wheel. Literacy allowed the Europeans to dominate most of the World. China had literacy, but it was the domain of a limited number of people, as it was in Europe before the printing press. Literacy makes any society superior to one that is illiterate. Advanced technology, even as advanced as a toilet or machine gun or steam engine, requires literacy. Would you really want to live in a society where no one had ever read a book?