Bernie couldn’t perform as well in the South which is a major voting block.

Major voting bloc in what, the primaries? Why is that even relevant? Democrats don’t win in the South. That sucks if you’re a Dem voter in the South but basing who the candidate is going to be in a national election on winning some primaries in states that won’t go blue in that election is pointless. The South is a lost cause. There’s no reason to care what they think about the Democratic nominee.