Because it's really not too far from the truth. That is how ridiculous their opinions are and how slanted they really present things.
There was a cartoon on comedy central called Lil' Bush about six or seven years ago, featuring Bush, Cheney, Rice and Rumsfeld as kids, it was the same way. Funny at first because it's supposed to be a joke but it turns out that it's not a joke, that's really how it is.
Best part is their correction scroll. They have to usually go back and make a few minor corrections to the things they said during the first 2 hours. They go by so fast but they are usually priceless!