If your presidential candidate did very well in the last election despite losing, wouldn't you want him to run again? Not if he was simply a not much more palatable alternative to the other guy.
Despite the fact that I think a lot of the things the Swift Boat veterans said about John Kerry are exaggerated or false, I still don't think he would have made a very good president. (Truth be known, I didn't vote for George Bush either--for the same reason.)
Some people I know said that Kerry would have been a much better president than George W. Bush. Well, now's his chance--but he's not taking it.
John Kerry did very well in the 2004 presidential election. He came pretty close to winning. He should be this round's front runner, shouldn't he? Why then is he not even running again?
If he had to run against George Bush, I might be able to understand why he wouldn't want to try it again. But George Bush can't even run this time. Kerry could run against an open field.
I am going to go out on a limb and say that Democrats don't really like John Kerry. The only reason they put him to run against George W. Bush is because Howard Dean gives the occasional appearance of being mentally unstable.
In other words--most of the people who voted for John Kerry didn't really want John Kerry to be president. They just didn't want George W. Bush to be president worse.