One theory as to why we still have not encountered sentient life in the universe, is that their civilisation may have collapsed due to the same overexploitation of their environment like what we’re doing to earth right now. We think we are separate from nature and that we are taming it. But that is not the case. We are bunch of cells shaping the environment, who are no different to our cyanobacteria ancestor that exhaled and oversaturated the earth with oxygen millennia ago, causing mass extinction. The difference with us, humans, is that we are so smart we could accelerate the process of mass killing in a matter of only several generations.