"Talking out of my ass here, but most of the Bernie supporters were Ron Paul 2012. Anti-mainstream establishment."
Ron Paul came in 4th with 11% of the vote, behind Newt G, Santorum, and Romney. He won a single state. 2 million votes.
Those supporters would have had to switch to Democrats for the primary election.
Bernie pulled in 43%, 13 million votes, and won 23/57 contests.
Completely different group of people.
You could probably safely say that most of the Ron Paul supporters were actually democrats, which is why he had a strong online following but lacked the primary votes.