True, Freemasonry does attract intelligent and driven men who leave their mark on the world and their contribution cannot be overlooked. But for every President or movie star, or other named personage, there are hundreds of Brothers who's contribution is just being good, honest and decent men.
As for why this is, my belief is that men that feel the way we do go searching. For some, it is the desire to know and associate with others like us since we do not always find those with the same values in our daily lives. For others, they may have a feeling that there is more they can be doing in their daily lives and go searching for a way to do that. For the lucky ones, they happen on the Craft and hopefully find what they are looking for.
Others have read of the accomplishments of great men and see the common thread that binds them and want to be a part of it, to feel connected to the greatness.
IMHO, there are so many great names throughout history that have the epithat of Freemason because we attract and breed a certain type of individual. Commitment, Service, Duty, Sacrifice, Honor, Integrity, and a sure knowledge of the importance in a belief in the Divine.