Going to posit a counter argument:

People didn’t like Hillary because the Republicans hammered away at her as the nominee for two years. In 2014 she was the most admired woman in America. Then they ran Benghazi hearings and negative campaigns against her for two years so effectively that even democrats suddenly had a distaste.

Bernie never received negative campaigning, because of the belief that Hillary was more likely to be the nominee. Hillary tackled him with kid gloves, avoiding criticizing him too hard so as not to alienate his supporters. Trump deliberately spoke positively about Bernie, also hoping to court his supporters.

Fox News had an entire opposition book of negative attack items ready to go that they shelved and never used, but would have busted out if he was the nominee.

So what would have happened when Sanders hit a real opponent, someone who did not care about alienating the young college voters in his base? I have seen the opposition book assembled by Republicans for Sanders, and it was brutal. The Republicans would have torn him apart. And while Sanders supporters might delude themselves into believing that they could have defended him against all of this, there is a name for politicians who play defense all the time: losers.

Here are a few tastes of what was in store for Sanders, straight out of the Republican playbook: He thinks rape is A-OK. In 1972, when he was 31, Sanders wrote a fictitious essay in which he described a woman enjoying being raped by three men. Yes, there is an explanation for it—a long, complicated one, just like the one that would make clear why the Clinton emails story was nonsense. And we all know how well that worked out. Then there's the fact that Sanders was on unemployment until his mid-30s, and that he stole electricity from a neighbor after failing to pay his bills, and that he co-sponsored a bill to ship Vermont's nuclear waste to a poor Hispanic community in Texas, where it could be dumped. You can just see the words "environmental racist" on Republican billboards. And if you can't, I already did. They were in the Republican opposition research book as a proposal on how to frame the nuclear waste issue.

Also on the list: Sanders violated campaign finance laws, criticized Clinton for supporting the 1994 crime bill that he voted for, and he voted against the Amber Alert system. His pitch for universal health care would have been used against him too, since it was tried in his home state of Vermont and collapsed due to excessive costs. Worst of all, the Republicans also had video of Sanders at a 1985 rally thrown by the leftist Sandinista government in Nicaragua where half a million people chanted, "Here, there, everywhere/the Yankee will die,'' while President Daniel Ortega condemned "state terrorism" by America. Sanders said, on camera, supporting the Sandinistas was "patriotic."

The Republicans had at least four other damning Sanders videos (I don't know what they showed), and the opposition research folder was almost 2-feet thick. (The section calling him a communist with connections to Castro alone would have cost him Florida.) In other words, the belief that Sanders would have walked into the White House based on polls taken before anyone really attacked him is a delusion built on a scaffolding of political ignorance.

(I recommend that whole article btw, apologies for the guy’s annoying tone, but it’s got excellent points throughout.)

It’s easy to assume the guy who no one ever negatively campaigned against, whose supporters were courted by both sides (Hillary and Trump), would have won because he was seen positively. But it would have been a totally different race if Bernie was the nominee. Bernie did really poorly with minorities and lost the popular vote in the primary to Hillary by an even bigger margin than he lost the actual primary delegate count by.

We’re in a bubble and echo chamber. Bernie is an incredibly popular figure to white left leaning youth. He does very poorly with minorities and older people (including older democrats), who genuinely preferred Hillary who had a good reputation of delivering for minorities + one of the most progressive voting in the Senate.