Ultimately this question is the question of why the universe isn't completely isotropic in all directions with a completely uniform distribution of matter and energy. To the best of our knowledge this is due to quantum effects at the beginning of time creating a temporary asymmetry whose resulting "sloshing" created everything more complicated than evenly-distributed hydrogen gas. Life on earth is the tiniest swirl of complexity in the vast waterfall of "wasted" entropy that is the sun burning out.