What Dems can't seem to understand is that Bernie was NEVER going to get the Democratic Nomination because he's NOT A DEMOCRAT.
The Presidential Nomination is the biggest award a party can give to a candidate. It essentially puts them at the head of the party. Bernie is a card-carrying Independent. He is NOT a member of the Democratic party. The party (The DNC) wants reward their own members, and give the nomination to a party member who has been supportive of the party over the years, and gathered the support of most of the country.
But Bernie has never been a Democrat, and is often nearly as critical of the Dems as he is of MAGA. He might caucus with the Dems, but he doesn't raise money for them, his agenda is entirely different, and his successes are not their successes. The DNC feels about him almost the same as they feel about a MAGA candidate, or any candidate from any other party.
How would you feel if a Libertarian hijacked the DNC's infrastructure and forced the party to support him, just because he got a bunch votes under their banner? He doesn't like you, he doesn't hang out with you, he doesn't help you, he just called himself one of you so he could run, and he has no intention of following any of your policies. He's just using your party to get what he wants, without regard to what the party wants.
Now, when it comes to the corrupt DNC, ALL of that sounds great to me, but it's terrifying to the DNC. At the time, it came down to having two candidates - one who has dedicated their life to the party, and who has an excellent resume, including 8 years in the White House already, or a popular outside interloper who is trying to exploit the system for their own personal gain.
Take out the emotion of Bernie getting screwed, and you can understand why the DNC made that decision, even though we hate it. And guess what? They'd make that same decision 10 out of 10 times. They simply won't give their precious nomination to an outsider.
Edit: Yeah, I get downvoted for this opinion every time I express it, but it's true, and we all know it.