...because they showed up at the White House, in a bus,
uninvited.
(Thus spoke NPR just a moment ago.)
Don't let him get away with that! Spread the word!
[Update: This is confirmed in a Fox News article, of all places.]
[Update2: thebes provides a letter from Elijah Cummings, the head of the CBC, which points out that as of July 2003, "...the CBC's requests for meetings with [the Bush administration] have gone unanswered for more than two-and-one-half years..."
]