The primary dates are not as traditional as they used to be. All the states want to cut to the head of the line.
Hillary Clinton and Joseph Lieberman were also early favorites - based on name-recognition and nothing else. If Dean lead in polls, it was because he had conducted a different kind of campaign. He ran primarily on the internet and word of mouth. It didn’t mean he was a better campaigner, he just didn’t stick as much to the states themselves.
It would have been a bad thing. The primaries, for all their faults, are a process. You see who’s initially appealing, and then that guy becomes a target. You see how he deals with the scrutiny, the pressure, and the attacks. If he comes through and is still the most appealing, he should win. If not, he drops down in the running and someone else gets a shot. You need the primaries to be spread out so the whittling-down can happen. Otherwise, the only option is for an exhausting redux of the general election, only with maybe half a dozen candidates instead of two. And what do you do if nobody gets a clear majority? Still more primaries? Everyone would be exhausted by the end, and that much campaigning would probably screw the nominee.