One would think that as the human race has evolved and with all the technological advancements we've made it would mean people as a whole are getting smarter. But it's things like this that make me wonder if it's only a very small percentage that are getting smarter and the rest of society is getting dumber.
Maybe there's only so much intelligence available in the world, and for someone to get smarter, one or more people have to get dumber?
Taking an outsiders view: Just having seen 2010s Crime Statistics for European Countries and the USA, my guess is that the citizens of our worlds only left super-power simply decided to annihilate themselves.