Final answer:
Gods from various beliefs decided to exterminate mankind due to different reasons, ranging from being annoyed by humans to punishing wickedness and corruption.
Step-by-step explanation:
The reasons gods agreed to exterminate mankind vary across different mythologies and religious texts. In Mesopotamian myths, gods, like the storm god Enlil, considered destruction for reasons as trivial as being disturbed by human noise.
The biblical God's decision to send a flood, as depicted in the book of Genesis, was due to wickedness and corruption among humans. In Zoroastrianism, the god Ahura Mazda created a good world which was in constant battle with the evil of Angra Mainu.
Humans were given free will to choose between good and evil, with the understanding that their choices would lead to judgment and potential punishment.