Why was military dominance among the Banu Abd al-Muttalib before Islam?

Banu Abd al-Muttalib did not possess military leadership before Islam; rather, they held the right to provide water (siqaya), because Abd al-Muttalib was the one who dug the well of Zamzam. It is reported in Sahih Muslim that the Prophet, peace and blessings be upon him, said to Banu Abd al-Muttalib, while they were providing water at Zamzam: "Draw water, O Banu Abd al-Muttalib! Were it not that people would overpower you in your right to provide water, I would draw with you."