Earth was humankind's headquarters, but unlike other species, its security and defenses were full of holes. That didn't apply to its orbit, but the planet's surface was a different story altogether.
Much of Earth's surface had yet to be reclaimed by the Global Army. The First Impact had left the planet deeply scarred, and humankind had aimed for the stars after regrouping into families and organizations. The universe was far more lucrative, so the humans had ignored the many vast territories that were too expensive to restore.
Needless to say, the security and control over those territories were non-existent. The Global Army only cared about the big cities, even ignoring the Slums around them, so their scanners never pointed at those abandoned lands, making them perfect for criminal activities.