It's not the place for the Theory of Evolution to explain the origin of life, as the theory explains the diversity of life from common descent.
The origin of life can be reasonably explained away as a chemical reaction that is no more miraculous than a baking soda volcano science project, actually. Do we have evidence for it? Not exactly -- that's why abiogenesis is still hypothesis.
The reason why our explanation happens to be a naturalistic one is because any explanation for anything we know thus far about the universe has naturalistic explanations behind them. There's no rational reason to assume the supernatural is responsible for anything or even exists at all, for that matter.
But see, rather than making the assumption that we know it for fact, we continue to study it until we know more about it, and then keep studying it still. Unlike creationism, which is takes an anti-knowledge stance by saying "God did it, that settles it, there's nothing to learn here."