Independents, needed to win the general, were not permitted to participate in several major Democratic primaries. Those Independents did not go for Clinton (clearly). Nor did Millennials, who also sat out for Clinton.
If you need people outside your party to vote for you, you don't restrict caucusing to just your party. Otherwise, you get the proverbial brick in the face. Must be a terrible legacy to lose to the person that makes up Trump in front of the entire world, that people said to themselves "Yes, he's a bigot, a xenophobe, a sexist; but he's not Clinton" as they voted.
@fatbird: I'm unsure why we're still arguing about this. Clinton lost because she did not have enough support, period.