Plus, the world is already on the right track. It only needs guidance to keep it away from the dark forks in the path we travel together. To uproot all of that... what purpose would that serve? Personal satisfaction? Hardly worthy.
Taking over a world is a lot of work. Just trying to maintain a stable worldwide economy between groups that have always been opposed to each other, quelling uprisings, hearing the people's pleas (or ignoring them), it'd be very tiring.