Agreed that Hillary played race games to try and beat Obama which probably explains a good amount of the shift. But the PUMA crew seems to have been forgotten even though they were the equivalent to Bernie bros (race instead of mysogyny).
People United Means Action - Wikipedia
As far as voters staying home, I'm fairly certain the polling later on showed Obama supporters did a lot of staying home (I remembered to look around for stories on it because I legit blamed the whole PUMA crap from Hillary's failed primary).
What Happened to the Obama Coalition? | VOX Global
Basically, the data I've seen has always seemed to point to Bernie voters being singled out for behavior that's commonplace for supporters of other candidates. But it got exaggerated thanks to the close nature of the race and became a narrative that ignored other relative examples. The other thing on Bernie voters staying home that I rarely see acknowledged is that he got a big boost from Independents who jumped into the party specifically to vote for him, that they abandoned ship after he was out seemed like a foregone conclusion (a significant chunk of these people actually turned on Bernie for even campaigning for Hillary after he lost).
Lemme add though, that I think both sides of the Dems will have a lot better understanding that this is too important to protest vote or risk a loss. But there's a subset of Dems that I could see stepping away if a Bernie or Warren won, since their policies could actually hurt that subset's pockets.