Because when a Republican somewhere, in some venue, criticizes Obama, it's news.
So Politico's Ben Smith rushed up a post yesterday after Minnesota's Republican Gov. Tim Pawlenty appeared on Fox News and called Obama's health care reform proposal "a joke":
Pawlenty blasts Obama plan
In the eyes of Politico pros that's news. It's important and it needs to be documented (complete with video!) for all the Beltway to see. The deep irony of course is that, from a journalism perspective, a Republican appearing on Fox News to attack Obama (about anything) is pretty much the opposite of news. It's ordinary, expected and predictable.
But at Politico, which seems to have been created in order to give Republicans a bigger platform at attack Democrats, the dog-bites-man sight of a Republican criticizing a Democrat (on Fox News, no less), has been elevated to a hallmark event and one that must--must!--be reported quickly, quoted at length, and treated as gravely important.