My theory is that the fallen once had the traveler come to their planet and they had a collapse but instead of being killed off they joined the darkness Forever leaving there home That's why they are siting up places on our other planets and have this rich background of once being a "proud and noble race" Also fallen can be seen working with the queen of the awoken So what if those original awoken teamed up with some of the fallen that didn't wanna help the darkness and just wanted to stay out of the dark and light battle.