Some did, but the Dean coalition was different from the 2016 Sanders coalition in being far more upscale. Dean did miserably through 2003-2004 among working-class Democrats of all races, and many polls showed him weaker than Kerry against Bush. His voters were mostly the "latte liberal" crowd, many of whom later voted for Hillary over Sanders.
This.
My uncle was a Deaniac at the time & even he admitted that, in retrospect, Kerry was definitely the better candidate. A lot of progressive firebrands were caught into the groupthink of the early netroots internet activism & missed that Dean was actually the latte liberal candidate & that Kerry had the support of the working-class base of the party & was actually giving rabble-rousing populist stump-speeches to blue-collar workers in NH. And yes, you heard me right: Kerry gave rabble-rousing speeches!
Funny thing is that this time it turned out Sanders was more of the latte liberal championed by progressive firebrands on the internet, while Biden had more appeal to the working class voters in real life. So pretty much the same disconnect occurred. The difference is this time some of these people were fooled into thinking Bernie had actual blue collar appeal based on 2016, but it's pretty clear now those were just anti-Hillary votes rather than pro-Bernie votes. And the funny thing about that is that in 2008, when most of the internet (that wasn't behind Ron Paul) was behind Obama, Hillary definitely won the WWC vote. It doesn't seem the internet progressives have ever actually been on the side of the working man the way they think they are.