Please describe the "fix" and how it would have been effective if young people had showed up to vote in the primaries for Bernie.
The problem here is that most states don't allow people who aren't registered as a member of a party to vote in that party's primaries. And Bernie attracted a lot of attention from independent young people who didn't want to affiliate with the Democratic party.
Like it or not, that independence bit them in the ass, because they could rally and chant and protest and send money to his campaign, but they couldn't vote. Meanwhile, more pragmatically-minded people who knew they couldn't vote in primaries without being registered as Democrats all lined up behind Biden, registered, and voted.
It didn't thrill me. Biden was last on my list, and my preferred candidate was Elizabeth Warren. Bernie was #2 on my list. But when I talked to my pro-Bernie friends, I knew - and so did they - that Biden was going to win, because his supporters registered and turned out to vote.
Since then, young people have clearly smartened up and recognized the same problem. They're showing up to vote in every election, and it's causing Democrats to overperform and beat the polls. I absolutely love to see that.