There are a lot of dems who do not want to lose again, particularly not as humilatingly and thoroughly badly as the Gore and Kerry candidacies were crushed. The chance that a Hillary try could go down in flames for a third Republican victory would be as bad for them as was the Reagan landslide victory that gave us two terms of Reagan and one of Bush I. A twelve-year absence of Democratic Party success at the executive level could get voters into the habit of thinking of them as losers.
And that was why Howard Dean very wisely stepped aside and let Kerry take the door that slammed shut in his face after Dean's third-place primary finish in Iowa. And so now Dean is DNC chairman; neat.
I think also that there are even more dems that are sick and tired of the Clintons. They feel like we conservatives have for a very long time. "Just get the hell off the stage you money grubbing trailer trash so we can lysol all of Washington".