Why did Sanders's demographics change so much in only 4 years?

[Intell]

From articles and anecdotes;

The WWC that voted for Sanders are either Trump voters, non-voters and Clinton voters.

The ones that stayed with Clinton are now trending towards Biden.

The trump voters are either now just republicans or Trump Democrats (trump in presidential, democrats down-ballot, so they don't vote for Sanders. There is also a section of Sanders-Trump voters, who that would probably be their last vote for president, and they are now checked out of the political process after trump "disappointed them", and Sanders now seems "different' and more "woke". The trump democrats who turned back to the D fold are probably even split between Biden and Sanders.

The ones that were Sanders-non voters are clearly not as enthused about Sanders this time and are not voting at levels close to 2016.

I believe democrats will gain in WWC areas in 2020, but only because there are a subset of working class voters that voted for Trump but are now abstaining- resulting in democrats to do better- but no real vote switching in the presidential race.


Anecdote time:

So I know this guy who voted for Obama-Sanders-Trump. He had no preference between Sanders and Trump in 2016 but hated Clinton and the republican establishment. He was a registered democrat so he voted for Sanders hoping he would so he could select between two candidates that he broadly was ok with- who he voted for would have been a coin toss. Clinton won so he voted for Trump and democrats down ballot. By 2018 however he had given up with both parties and didn't vote in the midterms but he said he would've voted for democrats if he had to vote and in 2020 he isn't going voting for any candidate but if he has to vote he says he'll vote Trump-Downballot democrats.

I'd say that there are a lot of voters like these non-voters around, but if they were forced to pick they'd be republican all the way through rather than Trump-downballot democrats.