The best answer for why does the universe exist is what scientists have opined, and why all other universes exist.
All Hail the mighty and Omnipotent Scientists! Cast scorn on all doubters!
Without the “we” what difference does it make?
That seems so absurd. Scientists can't even get their own message across: everybody hates them so much whenever they say something unpopular, like on climate change. Your fantasy that the scientists rule the world is totally ridiculous. Rich folks like Trump or Putin rule this world.
But who are we to decide what the perfect climate is.
How does one reconcile the many political and religious' philosophies that are extent?
... the extinction of Homo sapiens could be good for biodiversity.
those "other critters" won't understand what's happening.