BaZi doesn't provide a moral explanation, but several perspectives exist:
Daoist view: The universe flows in patterns of Yin and Yang, surplus and deficit. Individual charts are expressions of cosmic diversity, not cosmic judgment. A difficult chart isn't a punishment — it's a different set of lessons.
Buddhist-influenced view: Charts may reflect karma from past lives, but this is speculative. What's certain is that this life's response matters more than the chart's appearance.
Practical view: "Good" and "bad" are often misjudged. A chart with enormous gifts may also carry enormous pressures. A "weak" chart may develop profound wisdom and character. Many people labeled "lucky" by outsiders carry burdens no one sees.
The deepest answer: the question itself assumes a fairness that the universe doesn't promise. BaZi doesn't explain why you got your chart — it shows you what to do with it.