Gamblers House, a blog dedicated to work on Chaco Canyon, goes into some common questions they get from visitors. 
One thing that seems to surprise a lot of visitors is the fact that the Chacoans apparently had no knowledge of the wheel, or if they did have such knowledge they didn’t apply it to transport any of the many things they brought into the canyon from distant sources.
Answer; a lack of draft animals.    It's cool stuff.

Now tell us why so many of the New World civilizations learned to write either.