Because the Observer is confused be sure the Universe is it NOT.
The Universe Reality don't care about the Confusion of the Observer, and more it does not care about the mathematical concepts of a confused Observer. The Universe don't calculates probabilities, it Knows the state of the cat. Only an Confused Observer needs a collapsing wave function to get a information what in essence existed prior.
Maybe just maybe it is easier to get over that confusion, instant to write math that try to prove the confusion is reality.
IT IS NOT, IT IS YOUR CONFUSION