We may have different ideas of what sort of answers a "why does this phenomenon occur?" question deserves. You seem to be looking for a real phenomenon that causes fine-tuning, or which operates at a more fundamental level of nature. I would be satisfied with a simple, plausible fact that predicts the phenomenon. In practice, the scientific hypotheses with the greatest parsimony and predictive power tend to be causal ones, or hypotheses that explain observed phenomena as arising from more fundamental laws. But the question of where the fundamental constants of nature come from will be an exception if they are truly fundamental and uncaused.