A stumper has been why the Mayans, for whom wheels were both sacred (in the forms of their calendaring and astrological systems) and mundane (in the form of wheeled childrens' toys) never 'discovered' the use of wheels as a tool for facilitating transport. No wagons. No hand carts.
In the future, what will they look back on us with disbelief saying "how could they have missed THAT application of technology?"
At least now you can get Maya wheels.