[Surah Al-Qalam 68:4]
How Paganism (polytheism) thrived in Arab - Throughout their lives, Prophet Ibrahim and Ismail (peace be upon them) promoted Touhid. After their death, as years passed by, evil practices spread out in Makkah though Touhid was intact. Amr bin Luhay was a well respected merchant from Makkah who used to travel widely to buy goods . Once he traveled to Sham. He saw people gathered at a place and a huge idol. People said that they were invoking the idol to intercede on their behalf to Allah to send rain upon them. Amr, the ignorant, asked for an exact copy of the idol and brought it to Makkah along with goods. This was the first introduction of shirk to Arab. He introduced it to the people of Makkah as an intercessor to seek rain. Soon idol worship became rampant and then small copies of the idol were made. Deen was distorted and during the Hajj, when more Arabs came for Hajj, they saw a change in the culture of Arabs and they too, were introduced to idols.
This is how the shirk spread. Soon, every rock and stone of Makkah was considered to be sacred by the visiting pilgrims. Thus the religion deviated from the righteous, straight path.