What did the Aztecs or Incans among others have that the Apache, Navajo, Sioux, Cherokee, Haudenosaunee, Ojibwe, Haida Gwaii or even Inuit not have to faciliate Empires.
This is a frequently asked question, so while waiting for our scholars to dive in check out these previous answers...
What constitutes an empire? One definition goes "an extensive group of states or countries under a single supreme authority, formerly especially an emperor or empress." If it was just a matter of area controlled by a single political entity, I would give the example of the Nehiyaw Pwat, the area controlled by the Iron confederacy of the Cree, the Assiniboine, the Metis and the Saulteaux. The difference is that even these groups, who actively pursued taking over control of trade in new areas, were very much committed to decentralized control, and to interacting with each other on a largely equal footing, the opposite of what is implied with the word Empire.
\u\The_Alaskan in the response linked showed many of the ways in which First Nations and Native American groups had many of the values and institutions we strive for today. Many of these rights have been won through long fights with antagonistic governments. These are fights that people without these centralized systems (i.e. the ones that lead to empire) did not have to have.
In the specific instance of the Nehiyaw Pwat, even though they were a group that did fight for territory, they valued a political system that was different - a strong centralized leadership of the type present in empires would not have been a step towards what they wanted in life, they were better served by far more communal forms of decision making, even though they did at times rely on strong leaders.
In summary, another way of asking your question would be "what did the Apache, Navajo, Sioux etc have that the Aztecs or Incans didn't have, that allowed them to achieve their goals without the sacrifices needed to create an empire."
When it comes to making choices about governance, it's as much about choice as it is about resources at hand, and the same resources do not always lead to the same cultures. \u\Reedstilt described some fairly large centralized complex heirarchies that existed in the same location as later decentralized far more egalitarian societies, despite having access to the same natural resources.