Democratic Primaries

At the heart of it all, in my opinion, is that Sanders has been elevated from "presidential candidate" to the leader of an entire movement that is firmly centered around Sanders. As such, there's probably more of a personal emotional attachment to him for many. To many, he *is* the movement.

Also, by frequently distancing himself from the party, he's created a false sense that only he can solve everyone's problems and only he addresses issues. Those who believe this also tend to believe that should he fail, no one else will address the issues. In reality, many of the candidates this cycle, including Biden, and many, many Democrats have been addressing and fighting for similar issues for decades.

Again, when the candidate fails, there's further to fall because some believe he's the only answer to everything. For the rest of us, we understand that all of our candidates support many of the same things and have similar goals, so when our preferred candidate drops out, we know that the remaining candidates are still mostly in line with our beliefs, especially when compared to the binary choice in November, Donald Trump.

That's not saying that the supporters of other candidates don't go through similar stages or have similar reactions. It just seems to be more, shall we say, intense among supporters of Senator Sanders.