alt Hacker NewsMy point is that they didn't meaningfully embody collectivism even when they were younger. Collectivism is rice farming culture. https://www.sciencedirect.com/science/article/abs/pii/S00142.... You work together within a rigid social structure and share communally in the proceeds. But you have to precisely follow your socially prescribed roles because that system only works when everyone does what they're supposed to be doing. This is true even in developed countries that are more collectivist. Subordination of the individual to the collective is a big deal in Japan and Scandinavia. In both places, it's taboo to stand out in the crowd: https://en.wikipedia.org/wiki/Law_of_Jante. Individualism is necessarily in tension with collectivism and socialism. Individualism promotes status competition, and when status competition exists, communal sharing in the proceeds of collective labor becomes impossible.
American millennials were hyper-individualistic and rejected socially prescribed roles even when they were young. What they wanted wasn't collectivism, it was a higher status within capitalism. Which is why, as you observed, the sentiment evaporated once they achieved that status. I'd make the same point about Gen Z. They want to think they're socialist and collectivist. But they all want to be online content creators and influencers--jobs that only exist in hyper-consumerist, capitalist societies!
This is not a criticism either of collectivism or millennials, by the way. I think Republicans screwed up the concepts during the Cold War era by successfully labeling Democrats as collectivist. What you have in the U.S. is more accurately described as two strains of libertarianism, one that emphasizes social liberty and the other that emphasizes economic liberty.
I think you may be focusing on this with a lens that isn't incorrect—and is in fact very worldly—but which fails to account for individuals' behavior on their own terms.
You define your own notion of collectivism and make claims about how it is necessarily in conflict with other principles, when in reality millennials aren't a monolith, collectivism isn't a monolith, and individualism isn't a monolith. Cultures and subcultures renegotiate the meaning of every -ism they import, and they practice these -isms only as bundles of other, historically correlated -isms.
When the American youth say they want collectivism, they are not saying they want a return to authentic rice farming culture. Most of the time, they are mourning the systematic loss of third places, they are mourning the obliteration of social safety nets, they are mourning the lack of public projects, they are mourning the death of individually influenceable local politics. At the same time, they do not want rigid social roles ordained from above (because "above" is powerful and corrupt). They also do not want a parochial existence taking care of grandma (because the elderly are in greater number and need than ever, and our infrastructure and way of life is ill suited to efficiently meeting these needs). None of this is contradictory cosplay. It is simply a fusion of individualism and collectivism that is unlike that which has existed before, as a result of cultural factors that are themselves unlike that which has existed before.