What is a likely reason that the zhou leadership created the theory of the mandate of heaven?

In ancient China “Mandate of Heaven” also known as Heaven’s Mandate was the power given to someone on earth to rule the country by a superior power in Heavens. Zhou leadership changed the theory in their favor to get that power to rule by claiming that the former emperor had used the power for wrong or personal reasons which actually was not permitted to any ruler by the same theory of “Mandate of Heaven”. 

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