Complacency, pure and simple. It was significantly boosted by the fall of the Soviet Union which left the US as the sole superpower. Prosperity and technology have insulated us from the consequences of our actions & decions. We have had it so good for so long in this country that we forgot what pain really feels like. People embrace Marxism and denigrate Western culture because they percieive there’s no risk to it. While 9/11 briefly woke us from the slumber, it wouldn’t last. Seven years later, we were willing to elect a Commie/Muslim sypathizer as POTUS. Compared to Obama, Clinton looks like Eisenhower.
So, in short, we are victims of our own success.
It was the result of a takeover of our entire culture (media, education, entertainment industry, arts, etc.) by idealogues who never sleep,never give up, and never admit that they just may be wrong. It is a cultural virus that feeds on human desire for equality of results in human actions, which is a complete fantasy. Nevertheless, it sounds good, and in a brainwashed culture, that’s all that matters. Over 100 million lost their lives in the 20th Century to this fantasy, and it made no difference whatsoever. It will take a complete financial collapse to wake the public up, and that could prove to be very violent when the makers run out of money to feed the takers. And as history has shown us, societal upheavals never end up the way anyone predicts (French, Russian Revolutions).
Nero recognized this human condition in the 1st Century, so he burned Rome (to start things over and reset them to his liking), then fed the masses with handouts and blamed the fires on the Christians. Sound familiar?