Some theories on the fallen lore is that servitors are products of the traveler when it took a stand with the fallen in their home universe. Servitors were the voice of the traveler to the fallen therefore looked at them as gods. The purpose of the servitors were misconstrued by the fallen and then the fallen inadvertently fell to the darkness along with the servitors. Which is exactly why the fallen show the most interest in the traveler; because they blame the traveler for blindly following it into the darkness. Servitors are the equivalent of ghosts to the fallen is what I'm getting at, but their purpose was corrupted. EDIT: it also explains why the fallen rebuild fallen servitors. They can't build new ones because they are a part of the traveler.