Kaddi has low gravity for a planet of its size, which proved a significant boon to early quarian explorers. Even before the discovery of mass-effect technology, it was easy to extract Kaddi's resources. When the quarians made first contact with the Citadel species and gained access to eezo, profits rose and the orbital stations became a beehive of activity.
Today, Kaddi's Lagrange points are littered with space junk, including pieces of a geth orbital station that must have massed at least half a billion tons. Such a station could have generated impressive kinetic barriers, but even these appear to have been insufficient against the quarians' attack.