As politics become increasingly national instead of local, the theory that Democrats must have a single unified message is starting to look more and more valid (unfortunately). It is/was an extremely popular stance among leftwing millennials and progressives.

The only problem is that it's a stance in direct contradiction with those groups' preferred policy positions and messaging. We can't win swing/conservative districts with AOC-type messaging, as evidenced by the fact that no one ever has (or has even come close). So they've spent years insisting that Democrats need one consistent brand, only to make the best case ever that they're the ones who'll need to change their messaging.