I can't answer for others, but I've been a fan of Bernie's since 2009 and his efforts at adding a public option and moving the conversation to single payer. It can be hard to encapsulate or articulate nuanced positions within the confines of a forum post and across numerous threads.
I'm perfectly fine with Hillary Clinton not being the nominee, I'm no huge fan of the Clintons and I was one of the young voters Obama energized in 2008. Within the context of the Republican primary, the Democratic primary and Hillary's relatively strong position serves as a good foil for the disorder caused by Trump. If the Republicans hadn't been co-opted and we had seen Booker, Biden, Kaine and Warren also run, I think I would have preferred Warren to win.
Bernie's not my ideal candidate in this primary because of his comparative lack of detail in his policies, his focus on rhetoric and the identity he's presented during this cycle.