I have two theroies about why kerry lost. Well, actually three but one would make you get out your tinfoil hats
1. Kerry tried to pull a clinton and went hard after the young voters 18-24. for most of them this would be thier first election. This is the same demographic that put clinton in the first time. He went after them, got many of them to register. MTV and many big celebs joined him ( Bruce, Pdiddy, Drew Barrymore etc ) and they expected a big turnout and this to carry him into the white house. And on election day the 18-24 year olds stayed home. only 1 in 18 people in that age group voted in this election. And that killed kerry.
2. the Osama tape. When osama showed up again only a few days before the election it quickly reminded us that he is still out there and terrorism is still a very real threat. I think there were a lot of undecided that at the last minute thought of that and voted for bush. I, for the life of me, can't figure out why people think he has/will done/do a good job protecting us and fighting terroism, but they do.
So I think those 2 things really did Kerry in.
the 3rd one involves the voting machines in florida and things like that which may seem far fetched but might have a ring of truth.