As stated on the SandersforPresident Subreddit:
Hillary Clinton's main problem is that such a high proportion of millennials are intelligent enough, curious enough, and well-informed enough to see right through her piles of bullshit. She is really really smart, but we happen to be smarter. Also, Millennial values intersect with Bernie Sanders' values so well. We care about attention to detail, truth/integrity, curiosity, flexibility, and optimism with a future-oriented focus. That practically defines Bernie to a tee. I also think the vast majority of millennials have certain skills in more abundance than our predecessors. We are capable of deeply understanding nuance/shades of grey. We also seem to be able to hold two conflicting ideas in our minds at one time, and realize that both can be true, even though they seemed at odds on face value. All of these characteristics help us to see Hillary for what she truly is, and help us to see why Bernie Sanders is so rare and amazing.