Mostly because of a very successful propaganda campaign by people who sought to loot the post-war economic boom
Generally speaking, the sad truth of a complex economy is that coordination is hard, and there's usually a short-term privatized gain to be had by someone willing to poison the future and the commons. No amount of benefit to humanity overall or even the specific society such a person lives in will convince a person who simply doesn't care about anyone else. Fortunately for humanity, a very small minority of people actually operate like that. Unfortunately for humanity, some of them have managed to accumulate a lot of power
Generally speaking, the sad truth of a complex economy is that coordination is hard, and there's usually a short-term privatized gain to be had by someone willing to poison the future and the commons. No amount of benefit to humanity overall or even the specific society such a person lives in will convince a person who simply doesn't care about anyone else. Fortunately for humanity, a very small minority of people actually operate like that. Unfortunately for humanity, some of them have managed to accumulate a lot of power