Frankly because Kerry didn't present a strong enough case for voting for him. He wussed on his war record when he should have gotten angry, his wife seemed a bit too crazed, and he came off as too liberal. A study of the voting record in the US for the last 20 years will show that while the DNC tends to pick more and more liberal choices for president (Bill Clinton was an abberation in that regard)the voting public are usually aligned middle to middle right. Until the DBC realizes this, they don't look likely to get a person into office unless the GOP makes an extremely bonehead pick in '08 (this seems unlikely as the option field is looking much better this time around with McCain, Powell, Rice and Guliani--all of which still have enough time to distance themselves away from our current president)