If you come from wealth, it's easy to get into a good school, and your parents can subsidize you while you're launching your career (or outright create a career for you).
If you don't come from wealth, and you get to a city, and you start making over $200k, it's hard to even take advantage of it.
Instead of having parents to subsidize me, I have parents who are pretty broke and in bad health. How can I justify buying a modest house in my area (for $1M), when my parents are piling up debt, struggling to pay rent, and barely able to buy groceries?
Flip that even further to people who come from really poor countries like India. I can't imagine if my parents were working $1 an hour -- how could I pay $3k in rent? How can you invest thousands of dollars in yourself when your parents don't even make that much in a year?
But if you don't make those investments, you're never going to get ahead...
It's not just that wealthy millennials have a huge advantage, but coming from a poor family has a HUGE disadvantage in terms of social mobility as well.