Archaeologists continue to discover more and more about these civilizations that you seem to want to dismiss as irrelevant. What the Aztecs and Incas may have contributed to the world was mostly lost. What we do know is that they were not primitive peoples. The Aztecs had very evolved mathematics and medicine that we are still learning from. Aztec education was an important part of their culture. The Aztecs were very advanced scientific thinkers and mathematicians. The Aztec number system was far more advanced than other cultures at the time. In addition, Aztec science relied heavily on math, reflected in the design of their calendar. Aztec astronomy was also an important component of their calendar, which reflected heavily on their gods.
European invaders were impressed with the 10,000 miles of paved roads of the Incas along with their metal works, stonework, and cloth. Their buildings were constructed from huge stone blocks fitted so precisely that no mortar was needed to hold them together, many of which have withstood countless earthquakes and continue to stand to this day.
Both cultures had sophisticated farming methods and while the function of the wheel had not escaped them, not having any indigenous beasts of burden, it was relegated to use in toys. What they could have contributed to global knowledge is mostly lost except for bits and pieces being unearthed save for the few human remnants of their societies who have handed down some of that medicinal knowledge within families.
All ancient civilizations were not so utterly decimated in a few short years, but rather their peoples migrated, carrying their knowledge and traditions with them to new civilizations repeatedly throughout time. To believe otherwise is rather obtuse.