It could also just be their resources were insufficient and they plateaued or fizzled out before escaping their own planet was possible. Or that the distances

It could also just be their resources were insufficient and they plateaued or fizzled out before escaping their own planet was possible. Or that the distances and difficulty of transporting anything very large or complex between star systems turns out to be just too great of an engineering problem for any life form. The energy required to move a life-sustaining amount of mass between stars is mind-boggling huge and beyond our own technological capabilities for the foreseeable future ( we only anticipate interstellar life is a possibility by assuming our technological growth curve will continue unimpeded and then guessing there's life out there further along tha us, which may not be accurate or possible). Or that they are indeed spreading but doing it in a way undetectable to our technologies we're looking with and we just didn't come up lucky enough to be directly contacted by them in their spread (yet?). Or maybe they developed a Matrix-like utopia, a self-maintaining and long lasting support system and stopped outward appearing progress? Or going in another direction, perhaps we really are inside a simulation and $life_bearing_planet is set to 1. The hypotheticals are nearly endless and not necessarily due to overtly negative outcomes.