There are a lot, and I mean, a lot of things to like about Bernie, but there is plenty to hate about him too. I get Bernie Bros hating this outcome, and there is a lot of be disappointed about, but Bernie, and definitely more specifically his supporters definitely to me are classic have it right in the big picture, but absolutely zero realistic path to make it happen. It's definitely clear there are major issues, pandemic aside, with the US, and this pandemic is only massively exposing them.
However, he has hardly any key allies save like AOC and Omar in the house, and maybe Liz Warren in the Senate. But both he and his supporters are so voracious in their attacks of anyone who doesn't toe w/e line they have in their heads it pretty easy to go from wanting to support the guy to being swallowed up by the twitter and facebook crazies. Hell while Warren could go to bat for him she could just as easily take how she was treated by Bernie Bros and just not do anything, hell even AOC gets blasted by some of the zealots as a sell out occasionally. It's a classic inability to truly grow his base, and even if he somehow, somehow won the democratic primary, I would have serious reservations of him winning any key state he'd need to win (Wisconsin, Michigan, Pennsylvania) either better than Biden could, or definitely vs trump.
And even if he somehow won the presidency, a giant if, and even more giant if is how the hell would he actually get anything that he wanted done. Passing the ACA was practically political suicide in 2010, it would be even more so to try and do M4A, and hence much more reluctance from democrats this time around, let alone anything to do with college, or social programs he wants done, and I can just see the headlines for 4 years as virtually nothing gets done unless he makes concessions of "Socialist President can't achieve anything" and he'd probably be slaughtered in 2024.
Biden won because he had all the key support, was seen as a less extreme version of the 3 options on the table, and as you saw in Michigan it clearly seems especially in the democratic side Bernie made hardly any gains (actually made some losses) and it really shows just how hated Hillary was. You might not like Biden, but he doesn't elicit that vitriolic response.
The only thing that gets me about Bernie Bros is how quick so many don't want to vote for Biden, I both appreciate and respect that gumption to stick to certain principals, and think Biden doesn't have all that you want, but I never can understand how you would rather vote for some 3rd party candidate who is definitely not going to win, or not vote at all, all because you might only get a few things from one candidate, vs getting absolutely nothing from the other candidate, and then bitching about it for 4 years of just how terrible it is to get nothing. Would you rather have Trump appointing RBG's vacancy? What about having him in charge of IDK, a crisis like this? Even if Biden is starting to wane a bit mentally would you rather his cabinet helping him manage this vs Mnuchin, Ivanka, Jared? Are you tired of seeing the president of the goddamn US fight like a 5 year old with reporters cause they are asking him big mean questions?
I get the policy bits, I understand "you know what's better for this country so vote for Bernie goddamn it," but how can you be so ideologically pure that anything less comes along and it's not just not good enough, but it's practically seen as abhorrent
Being President is an important job no doubt, but it doesn't mean you live with that person, or you have to defend everything that person does, but then again you get in that mode I guess. Oh well.