They well not want major players in the adminstration on that often as they may well feel that it dilutes the impact when they are on.
Also they know that whatever they say it will be spun so why bother unless they want to say something really important that cannot be ignored.
Also I still seriously doubt how much they can insisit someone appears on a TV program. Surely that would be government controlling the media and the last thing they would want to be seen as doing this.
Depending on the democrat that these shows put on....I am sure the White House sometimes delights in the guests...
whenever Howard Dean gets on..with his nonsensical attacks, and Rangel, and Sharpton, they are SO over the top, that in my mind, they help the Bush Administration...
In fact, I think the interview with Murtha last Sunday did more to hurt Murtha and the dems...than the POTUS.