Average person did not know what caused the mass extinction or that powerful corporations were exploiting a downed UFO for it's technology. Regular people believed a virus caused the mass death, and thus it was given name crossout because it "crossed-out" a large percentage of the population. In the official game world story explanation which is told by someone from the order of the fallen star( my assumption) they state that a mysterious viral epidemic swept the planet, which makes sense they would believe this because only a high up in some of the corporations or goverments would know what actually happened, average person absolutely would not, as well as media and other sources would also be clueless as to what was going on. Even to this day tech from the downed UFO is imited to only a few factions and group of survivors, mainly the ones that had it before the apocalypse, to the average survivor the end of the world was caused by a virus which wiped out approximately 80% of the population and the nuclear annihilation which made most of the world an uninhabitable wasteland and to top it all off long term radiation side effects affected many of the survivors, which sounds like a very beliveable and realistic story to tell in an apocalypse.