The actual answer is: We don't know.
It's no longer surprising to me that arrogant people like A.Nonymous love to yell at people and tell us how stupid we ALL are in their attempts at analysis.
Such people can never ponder that perhaps Americans want their ECONOMIC concerns addressed and so it's not stupidity that drives there vote, but rather a realistic assessment that the Democratic Party has long abandoned the working and middle class in favor of the professional class.
One need only have watched the Democratic National Convention with its parade of neoliberal Republicans while denying time to any of their populist wing to recognize that this party doesn't REALLY care about us.
And that also speaks to the lie of the Democratic Party's narrative on Covid-19--they speak of all of these radical changes to the society because it's for "public health," but meanwhile don't support popular ideas like universal health care and giving Americans some financial stimulus beyond a one-time check (like most normal countries did).
Having said all that, considering how much the Establishment Democrats and their pals in the media hate Sanders and his ilk, it's likely they would have played some nasty tricks to keep down the vote for him, so, again, we don't know.
What we do know, though, is just like 2016, the People aren't all that crazy about the Establishment Democrats. And it's because they are a lot smarter than most give them credit for.