Even if they did nothing else but try and polish these huge stones, when would they find time to hunt and gather?

>"In the modern stone-art known as lapidary, it is very difficult to make a perfect sphere that is 2 feet wide. To manufacture spheres out of a hard substance that is 6, 7 or 8 feet in diameter...is building on a scale above what we can accomplish today."

On the other hand, we could look for a more natural explanation that they formed from a spewing volcano millions of years ago.....
>"The spheres were first “discovered” by US archaeologist Samuel Lothrop in 1948. Similar spheres exist in a remote ravine in the Sierra de Ameca mountain range in west-central Mexico, and Dr. Robert L. Smith of the US Geological Survey has theorized that these spheres were in fact fiery lava flows from some 40 million years ago."