You make a good point but in this election perhaps it oversimplifies the situation.  Most Bernie supporters have said they are Bernie or bust.  Indeed a fair percentage feel if they cant have bernie they would rather have trump over any of the remaining candidates.  Most of them dislike the rest strongly.    This is why Trump will win.  The Bernie bros will be denied the nomination, vote green, republican or stay home.  That is on average 25% of the democratic base up for grabs .