im pretty sure the enteriety of society didn ' t fall in left for dead 2 didn ' t that game end with the air force blowing up some bridge and the characters were rescued by the military ? they just fought to get to safety the whole gamein Extinction , you alongside every other country around the globe were fighting the aliens and failed horribly . They even dropped a shiton of nukes if I remember correctly . The human race was destroyed in Extinction with the only survivor being a girl sleeping in space . Even if it wasn ' t the case , there is no rescue , no helicopter to save the day . Even if there was again , those flying aliens have been shown to easily completely destroy helicopters from the inside out . Zombies can ' t do that . In Left 4 Dead 2 the human race was cut down significantly but it was definitely not annihilated considering a lot of people were still alive , uninfected , and other hospitals and countries were still standing .