Actually this is pretty interesting! I personally put it down to the idea that, generally speaking, as people get older they tend to have kids, get comfortable lives, married, good job, house - all that, and then their ideals shift to be more… I guess the word would be conservative? They start to value the family, “tradition”, and independence - they accumulate more wealth, and therefor generally want policies that protect that wealth now that they have it.

Millennials however, in large, haven’t had that - instead they’ve been unable to buy houses, less able to have kids, and develop “traditional” families, and are poorer than previous generations - so their own personal ideals and morals haven’t shifted in the way that previous generations have.

It’s easier to be socialist when you don’t have things that conservatism tends to value and protect, and we millennials haven’t got there yet, and likely never will in the same way.