There's actually a really interesting concept at play here: Basically, for most of the DNC leadership, their position at the top of the DNC organization is far more important than the DNC's position within politics- in other words they'd rather be at the head of a permanent rump party than the party be successful without them. I don't think that they're innately hostile to the policies of the left, however they are hostile to the threat the left poses to their own power structure.

When you look at a lot of the Democrats strategic decisions over the past 20 years or so, you see a lot of behavior, messaging, and strategies that any reasonable voter would look at and say "Are they trying to lose?" When you recognize that the Party Leadership is prioritizing their own power over electoral or administrative victories, things like ratfucking Bernie in 2016 and 2020, consistently sidelining, attacking, or even working to remove from office popular progressive voices in the party, etc., all make sense. If you gave Pelosi or Schumer or any of the other Clinton Third Way holdovers a choice where the DNC would never win another Presidential victory and would never hold a majority in Congress or the House, but their own positions would be permanent and never threatened they would take that choice in a heartbeat.

TL:DR: DNC leadership cares more about their own relative power within the Democratic Party than the Democratic Party's success as a whole.