We don't have to be unique, we might just be the next stop that has the resources. Maybe they're supernaturally interstellar and can move on. Maybe they're barely interstellar and can't afford to skip. Maybe nearly every earth-like has life and it's all deemed lower-ranking than this interstellar society. Maybe nearly every earth-like has life but this interstellar species has no anthropomorphic mammalian qualities and they don't care. There's no reason to beleive we can negotiate with aliens when humans largely do not respectfully negotiate with other species now. Hell, we don't negotiate respectfully between ourselves