87% of my generation stayed home. I'm going to fucking blame them, because they're morons.
Young people are mobilized by passionate big ideas that effect them, not pragmatism. The democratic party is all pragmatism and constantly being on the defensive. There is no talk in the dem party about free public tuition for college (or abolishing debt), there is no talk about at least 15$ minimum wage (now, not to be rolled out in 10 years where 15 will no longer be enough) or a basic income. There's no widespread talk of ending the drug war full stop, there's no talk of ending the surveillance state. Whether or not any of this passes congress is irrelevant, it's about being for something new and interesting if you want people to get out of the house and vote.
Young people care about this stuff and would vote for it if a charismatic, interesting, courageous party/people were willing to defend these ideas and challenge the right wing. Dems are unwilling to do this.
Until dems are wiling to go back to ideology, economic populism, and pro-civil liberties, young people will continue to be apathetic towards establishment democrats. To say republicans would be worse is simply not enough. This is not a problem on the right wing, where ideology dominates everything they're doing, and it's working. They don't have the young vote but they're capturing older working class people who should be dems, if dems had the balls to be anti-establishment.
If you want to gauge where liberal young people are at, it's someone like Russell Brand. Dems aren't talking like Brand except Bernie Sanders. Anyone who says only a center-right moderate dem party can get elected has a lot to prove after these results.