Why any species that considers itself so intelligent as to be worthy of colonizing neighboring worlds, or the stars, would paint itself into such a terrible corner, no-one knows. IF there were a god of some kind, they would most likely marvel at our human capacity for folly and fascination with large-scale industrial level death and destruction, and probably feel a little jealous, even slightly threatened.
As a teen I grew up under the threat of global nuclear war - it set the tone of my youth and given subsequent political and military actions around the world - the Gulf War, Sarajevo, the Balkans, Russia's war on Ukraine - even my adulthood. Humans don't seem able to choose a change from the way things have been since Hiroshima. Why can't things be different? Why must it always be thus? What if there was an alternative to the way things are? Surely there must be?
Let me offer you one.