He's acting like Bobby Kennedy that's why
That might be the reason. No matter what we all like to think, Dems aren't stupid. They want to win. If Edwards carries his own state (I know, that's not guaranteed) and everything else stays the same as it was in '00, he wins the general election.
The other thing is that Edwards has been running as the "nice" guy (which as a trial lawyer he's had a lot of practice at), while Kerry, Gephardt and Dean were ripping each other to shreds. That may have helped him.