This push would have been more helpful to the campaign pre-South Carolina, no? Or at least before Super Tuesday. Still, it's a must-do for anyone seeking the Democratic nomination, so it's something they absolutely should scale up.
This gets to the fundamental challenge of running against "the establishment." As @michaelharriot has eloquently written, for many black voters, esp in Republican-run states, their only power flows through their civil rights orgs and black Democratic reps, ie "the establishment." 
And these quotes by @MsLaToshaBrown get to a second point: Sanders' movement, unlike Jesse Jackson's 1984 and 1988 campaigns (which were similar platform-wise), has struggled to center racial justice as strongly as class justice. That makes his end-goal harder ie black voters.
