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!