it could be that only our brain exists, maybe only mine , not even yours. or not even that. mathematics and information and exustence are figments of the brain too. Existence is only defined as opposed to non-existence. But yeah, even though existence is indirect and subjective, it s OK to accept that it's true, since its not consequential

I suppose that s not a fruitful way to think about it but neither is asking questions about reason and purpose. Even if the universe has both of them, they are just 2 arbitrary points with a trajectory across spacetime.