Polytheism and idolatry are complex issues with not just one instigating factor but many factors contribute towards it. We find that some nations worship the sun, moon and the stars; some worship the fire and some consider large rivers to be their god like the Nile in Egypt and the Ganges in India. They considered all that were beneficial for them to be sacred and this so increased that they believed that it had a special soul and so they included them among their gods.
According to one explanation the idolaters lost themselves in the world of causes but forgot the God of all causes. This is because they did not have the intelligence or the sight that could discern the real cause for the existence of this universe. They were devoid of such thoughts that could understand the reality of causes. The result of their dependence on their whims and assumptions was that they became enmeshed in polytheism and idolatry.