The answer is:
climate conditions
other nomadic people
available food
As we now know, nomadic people only gathered what they were able from nature, and hunted what they found, they didn´t settle for long time in regions, nor grew fields, this is important because this led them to not develop several things that sedentaries societies did. They depended on climate conditions, other nomadic people, because of the competition for preys and gathering, and the available food in the place where they were.
