Because Bernie knew the system is rigged against him and thus allowed neoliberals like Biden to have their way. Now that the DNC lost pathetically to an orange man, and the DNC leadership is enabling fascism, I don't hear "vote blue no matter who" nonsense anymore. And Bernie and AOC have the last laugh and "told you so" moment to the DNC. Their tours are gathering record number crowds since Obama's 2008 campaign.