Randall has an idea of why there are no natives here. He spent the last few days reading up on the history. It seems that they (I have taken to calling them the Heteracerans) have been trying to fly. It is a religious thing. They are trying to fly to "the light" to gain salvation. It's a pretty easy bet that the disturbance that sent us here was just that - them flying away.
Still, you would think that they would leave some folks behind, just in case, right?