I think it just comes down to racism. Once the Civil Rights Movement happened all that collectivism disappeared because it had always been white supremacy masquerading as collectivism. Once all the diverse peoples of the USA were to benefit from that collectivism, the whites very quickly changed their minds about the socialist policies they’d put in place. Obviously I don’t mean the whites as if they’re a monolith, but it was enough of them to get the system to go in a different direction.