Your question presumes a linear, single-tracked progression of technology that does not accurately represent human history. Real life isn't Sid Meier's Civilization, where everybody needs to research the same technology along the same route. Inventions catch on due to practicality, and if a wheel is not practical, nobody's going to be looking to build one. "Unable" is a teleologically minded word that assumes some intention towards a results.

As for why, one commonly considered reason is the lack of pack animals. Wheels are only so much more efficient than other methods of human-powered transportation, but their usefulness soars when you add oxen, horses, or donkeys to the mix. The only domesticated pack animals in the Americas were llamas, whose ability to traverse difficult mountain terrain makes them valuable. Wheels render that trait useless.

You can find some more prior discussion on the wheel here.