The Giants were originally inspired by a daydream I had in 2008 in which colossal beings appear on Earth with no apparent motive or agenda. Most of our narratives around aliens or supernatural beings revolve around conflict - power struggles among equals. What would happen if there was no conflict? What would happen to our collective egos to know that these large and powerful beings were simply indifferent to us? In some ways, a child might be better at coping with this new reality, because they have no stake in their place in the universe.
Ultimately, the Giants became a metaphor for the things we find overwhelming - the anxiety created by the unknown that has the power to consume us. Transcendence, progress, technology, benevolence... but also patriarchy, authoritarianism, white supremacy. They represent perceived power - and sometimes, the impotence of that power when its source is revealed.