Bernie Sanders lacks charisma or speaking ability. He doesn't personally bring anything to the election other than a progressive platform that could be cut from the dailykos. Bernie Sanders is a generic progressive. You could put any name on the ballot. People are voting on his policies. And Democrats didn't vote for his policies yesterday. Some people will counter that the electorate was heavily African-American and they preferred Hillary Clinton. That's true, but African-Americans are an important part of the Democratic coalition. If they can't be convinced that voting for the progressive is a good idea then it's not a big sell to the Democratic party as a whole.
Certainly Hillary Clinton is running on her goodwill with Democrats. If the alternative to Sanders weren't well known and beloved by the Democratic party Sanders would've done better. But if you're starting a revolution then shouldn't some of those people choose it over the candidate who represents the Democratic party's moderate past. If people don't show up to your revolution then America isn't ready for it.
Barack Obama was the alternative to Hillary Clinton eight years ago and he won the Democratic primaries. Obama was no Sanders. His policy positions weren't all that different than Democrats since Bill Clinton and most of his plans weren't radically different than Clinton's were. In some cases he was to the right of her in the election. Obama won because he was charismatic and a great speaker who inspired the left to dream about the oceans receding and a better future. That a candidate can win based on his own charisma, as opposed to his policies, is nothing new. And Donald Trump is showing that this year.
We'll see more of how Sanders' message resonates on Tuesday and whether he can play outside of progressive White urban areas and college towns. If it doesn't, then even the Democratic party isn't ready for Sanders' progressivism.