Clinton was offering more Obama but with zero charisma.
Trump was offering something "different" (even if it was
obviously bullshit to us).
As brexit showed though, when people are in tough living situations (it's probably even worse in the US with so many homeless, no healthcare etc) they vote for extreme options, of which brexit and trump were two of. When people have severely ill people in their family, facing being put out on the street, going hungry, stuck on zero hour contracts, why on earth would they vote for even more of that from the same party?!
And from what I've read about the Dems since being wiped out is not much is different still, they want more of the same. They haven't changed their policies from what I've read and it's all been about Trump, Russia and blaming people who didn't get behind and vote for Hillary (I mean right now she is touring the country promoting a book she's just put out
Bernie on the other hand is touring the country and winning voters from Trump and pushing healthcare for all).