Why do we say that it was not natural fertility and high levels of food productions that were the causes of early urbanisation?

There is no denying the fact that natural fertility and food production were the causes of early urbanisation. Following arguments could be given in its favour:

(I). Natural fertility became the base of developed agriculture.

(II). Grasslands came into existence due to natural fertility which gave impetus to animal husbandry.

(III). Agriculture and animal rearing made human life permanent because now man became a food producer. Now there was no need for him to wander from one place to another in search of food.

(IV). When life became permanent then agricultural communities came into existence which started to live each other in huts. In this way villages came into existence.

(V). Higher level of food production led to exchange of goods. As a result, size of villages began to increase. New occupations were also started which were the indicators of urbanisation.