Why did Laura "insert" herself, by your seeming suggestion, into the show when she was part of a video montage for the Academy Awards? Why did George Bush and Laura "insert" themselves into American idol. It's not like they were "part of that business".
The answer? TV shows like to get a big catch like that, and those politicians realize that those shows reach a TON of people and can potentially be used to push a message, so when an option is presented to go onto American Idol to push for Charitable donations to the Military or to go onto the Academy Awards to push the benefits and importance of the arts for our youth, they take it because it's very little effort to reach a very large population...a population typically not actively engaging in political channels so sometimes may not be as easily reached.