Why is primitiveness the longest period in human history?

Because it takes a very long period of time, and also because the periods of history are usually classified according to the levels of development. So, in the primitive period, mankind was moving to a new level of civilization for a long time, and therefore, the primitive period of history will be the longest. This state of affairs is also due to the fact that the conditions for the prosperity of mankind in primitive times were not the best because of the ice ages.