Earth produces a long and prosperous civilization. After nearly all the resources are used up, the lean and hardscrapple survivors reason, "let's figure out how to squeeze the last bits of computation out of the environment so that our children will enjoy a better life than us before our species goes extinct". But from our perspective, those children won't have as much welfare as the vast majority of human lives in our future, so those children being born would bring our average down. We would will the hardscrapple survivors to not produce more people.