Why did Ray Bradbury write "There Will Come Soft Rains"?

It's good to know Bradbury's inspiration for this short story, for once you know it, you have a better sense of what is being related... the depths of the story's melancholy poetic exposition:

There Will Come Soft Rains

There will come soft rains and the smell of the ground,
And swallows circling with their shimmering sound;

And frogs in the pools singing at night,
And wild plum trees in tremulous white;

Robins will wear their feathery fire,
Whistling their whims on a low fence-wire;

And not one will know of the war, not one
Will care at last when it is done.

Not one would mind, neither bird nor tree,
If mankind perished utterly;

And Spring herself, when she woke at dawn
Would scarcely know that we were gone.

Sara Teasdale

So, as you see, the title of the short story is not original.
Neither, in many ways, are the ideas expressed.
In both the poem and the story, we are presented with a world in which mankind is absent and things go on as usual.

In the poem, life continues in its natural diurnal course.
And in the Bradbury story, similarly and ironically,
the manmade house continues to live and react in man's absence.

Why did Bradbury write the story? Why did Teasdale? To remind us that, in all our puffed up sense of self importance and propensity for self annihilation, in the larger scheme of things, we amount to very little. And if we should disappear altogether, we would not missed in the very least. Not by the birds or the frogs nor the things we have made for our pride and shelter, or convenience and our comfort. Let's hear it again:

Not one would mind, neither bird nor tree,
If mankind perished utterly