Exactly... They wrote nothing down and their languages were pretty much gibberish. So as far as linguistics go, modern generations are essentially making most of it up as they go along. They were stone age people when Europeans arrived with no horses, no metal work and they were essentially hunter gatherers... Without permanent residences and with no concept of ownership, wondering about the land and eating and existing on whatever they found. Writing wasn’t part of their existence until Europeans arrived.
The Mayans certainly had a written language, with an alphabet. and a calendar.
What you describe may have been true for most of the American territory, but in Central Mexico, and south into Central America, there were cities and people carving words on stone, and making a form of paper and writing books. The Spaniards destroyed most of the written material in the 1500s. Priests save a few Codixes, which are now very rare and valuable, and in museums or Spanish archives. There was also well developed agriculture. Some of the food and other plants developed here were sent back to Europe where they became widely use. Tobacco and potatoes are two.