In 2016, Clinton paid off the DNC’s debts and became it’s only financial lifeline, for which DNC chair Debbie Wasserman Schultz abdicated control of party to Clinton’s team long before she secured the nomination,, the AP controversially called the primary for Hillary just before California voted, giving voters the impression the primary was over before voting finished, and the DNC later argued in court that they had no obligation give Bernie a fair, democratic primary.

In 2020, Obama worked behind the scenes to get the other moderates to drop out and back Biden, and Representatives Ford and Smith admitted the party did coalesce around Biden in 2020 to block Bernie.

TL:DR: 2016 was meant to be a Clinton coronation with no real challengers, and they had to kneecap Bernie when he got in the way. 2020 was an open, fair election between everyone that wasn’t named Sanders, and they had to kneecap Bernie when he got in the way.

For one they did not, at all, care for the results of the votes. Like in 2016 they just used Superdelegates to invalidate all the races Clinton had lost.

Using the superdelegates to call the race for Hillary the night before the California primary, He’s in the superdelegates in West Virginia and other states. Doing everything they could to stop Bernie. Watch this clip: https://youtu.be/QGuVDz_88po

There was a primary in 2024 that Biden won as well. The DNC doesn’t need to spend much money on an incumbent’s campaign. It’s up to the voters to research their alternatives and vote in the primary. That doesn’t make it less fair, but suggests that US citizens are lazy or disengaged.