Because like Kerry, Dean, MacAuliffe, Clinton, Edwards, etc, etc, THEY ARE ALL DEMOCRATS! They want the worse possible light put on all things Bush & Republican. Like Clinton, they'll lie in order to see it done.
"THEY ARE ALL DEMOCRATS!"
There's more to it than just that. Most reporters today aren't really "reporters,", they are "repeaters." They dutifully repeat what they are told by their sources. Often, young "reporters" spend years developing inside-the-beltway contacts and protect their sources like they would protect their own lives - it's their livelihood.
Today, anybody who actually goes out and works a story has a new name - "investigative reporter." The trouble is, they should all work like that, instead of being hand-fed.