Because so far it appears that the non-randomness falls off sharply at macro levels. i.e., so far there seems to be no support for the idea that the universe i

Because so far it appears that the non-randomness falls off sharply at macro levels. i.e., so far there seems to be no support for the idea that the universe is actually chaotic in the mathematical sense from the quantum level to the relativistic one; Brownian motion doesn't change the weather. (I'm speaking specifically about the laws of physics in our geological era; the physics a few microseconds after the Big Bang would likely be different in this regard.)