DNC chair Perez's empty promises

He said he'd follow the DNC rules and bylaws, which require neutrality on candidates. Yet he won't abolish super delegates which explicitly violates that rule. He claims he welcomes progressives into the Party, but every action to date belies that. He's offered no concessions to progressives nor enacted any of their proposed reforms. So why do some progressives like Sanders and Hartmann continue to believe him?