"wheels" are useful/used in all sorts of things. For instance, wheels and vine ropes could have been used to give mechanical advantage for lifting huge rocks. Cranks and gears ... for stretching rope across canyons.
Evidently they very well KNEW about wheels and gears because they depicted them in their calenders.
http://www.smith.edu/hsc/museum/ancient_inventions/hsc08b.htm
But ... maybe they saw a taboo in using the wheel for anything but esoteric concepts?
-Vince
