But, the DNC is the establishment, so why would they do anything other than run an establishment candidate? And how much power does the DNC actually have over which candidate is run? That is decided in the primaries (see: RNC's control over which candidate was nominated).
They control the purse strings. The DNC could easily have given Sanders some dosh and infrastructure to get his message out. But the leaked emails clearly show they did everything they could to undermine his campaign.