Self-Improvement is not only to improve yourself from within but it is also about improving yourself materially too. In fact, self-improvement is such a topic which can improve yourself completely both from within and on the outer level.
It's obvious that you can't improve yourself only from within and not using the same process in the outer level in order to live a better life. If you don't do so, then you haven't learned anything. You haven't learned the lessons that your inner improvement wants you to learn.