In Polytheistic culture, gods fight and gods die. Zeus eats his (and thus kills) his father Chronos. Thor dies in Ragnarok.
In Monotheistic culture, the one true God is above all else. As it turns out, different Monotheistic cultures can then cooperate as it's an argument over what this one true God believes (Catholics vs Muslims).
Then we get into weird blends like Hindu and their many avatars of Vishnu (who'd argue that Jesus probably existed and could do those things because he probably was that time's Vishnu).
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Polytheism is likely flawed as an organizational concept because it's clear that gods were creations of man. Monotheism flips it and makes God the master of the universe while man struggles to understand the nature of God.
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But yes. As the sibling comment points out: the gods of most polytheistic cultures are NOT omnipotent or omniscient. They are more powerful or smarter than humans but they are still able to be killed or destroyed.
Maybe back when cities and religions would get wiped out by warfare, it was more common to see religions die out (and thus those old gods die with those religions/cultures). It makes you wonder about the nature of human belief systems and how humans lived differently back then.