The "why" is easy: he made too many people at the Post who were busy writing about how Saddam Hussein had nuclear weapons or how there is more sea ice than there was a generation ago or how "opinions on shape of earth differ" look foolish.
The Washington Post fires its best columnist. Why?: Froomkin was easily one of the most linked-to and cited Post columnists. At a time when newspapers are relying more and more on online traffic, the Post just fired the person who, in 2007, wrote 3 out of the top 10 most-trafficked columns. In publishing that data, Media Bistro used this headline: "The Post's Most Popular Opinions (Read: Froomkin)." Isn't that an odd person to choose to get rid of?....
In a post entitled "The WaPo's Best Blogger Is Fired," Andrew Sullivan writes:
A simply astounding move by the paper - getting rid of the one blogger, Dan Froomkin, who kept it real and kept it interesting. Dan's work on torture may be one reason he is now gone. The way in which the WaPo has been coopted by the neocon right, especially in its editorial pages, is getting more and more disturbing. This purge will prompt a real revolt in the blogosphere. And it should...
UPDATE III: Here is Froomkin's statement:
I’m terribly disappointed. I was told that it had been determined that my White House Watch blog wasn’t "working" anymore. But from what I could tell, it was still working very well. I also thought White House Watch was a great fit with The Washington Post brand, and what its readers reasonably expect from the Post online. As I’ve written elsewhere, I think that the future success of our business depends on journalists enthusiastically pursuing accountability and calling it like they see it. That’s what I tried to do every day. Now I guess I'll have to try to do it someplace else.
The Post's inability to articulate a coherent, credible explanation for what it did speaks volumes. Any media outlet is foolish if it doesn't strongly consider taking advantage of the Post's conduct by hiring Froomkin.