For the same reason you can find pyramids like structures around the globe: is the easiest solution and offers more stability.

The part of cities is debatable: sure mayas, incas, and Aztecs (and many others) had cities, as well as many others didn't, and all the instances in the middle.

Nobility is the natural evolution of a tribal society with different people in different roles. Was American nobility the same as European, African, or Asian? Well, there you have differences.

Irrigation, boats, and engineering is a response for having similar needs and materials. It's interesting that no American culture developed the Arch as the Etruscan/Romans did. They had the "Mayan" arch, that's a succession of stones in cantilever. Also, you can argue that the Incan work with stone was the best in the old world against earthquakes: basically they had a base of heavy stones interlocked, but not fixed, and on top of that smaller stones made the rest of the wall, with a lightweight roof. This prevented the collapse of buildings during earthquakes.

It's interesting to review the economic system the Incas had. Was not totally feudal, was not totally socialist, was not totally open market. Look it up, it's quite interesting. With it's upsides and downsides.

Also, the Incas didn't have writing as we understand it. They had knots registres.

Also, the Incas didn't use the wheel for carts. In part due to being very difficult to use in the Andes mountains, and also the llamas were not ideal as cart beasts.