Why do the centers of the diversity of cultivated plants coincide with the places where

Why do the centers of the diversity of cultivated plants coincide with the places where the great ancient civilizations were located?

Cultivated plants are the result of human activity. Until man began to cultivate the soil and began to grow plants, cultivated plants did not exist. All plants were wild. New useful properties of wild plants appeared due to artificial selection, which was carried out by humans. Ancient civilizations were already engaged in this, therefore there was a wide variety of cultivated plants. Nowadays, it is thousands of times larger, since we are engaged in breeding and genetic engineering.