Why? I'll tell you why....The aliens are cloning politicians, because they have little understanding of how the american political system works..They believe that the politicians have the power to get things done...In that respect theb aliens are rather like young republicans. And as for rockstars, the aliens needed a good way to send encoded signals to eachother when on earth. So by placing agents inside the bodies of rockstars, and using certain tonal frequencies and ranges, when the songs were played backwards, the messages would be sent (they learned this trick from their leader frank zappa).

Anyway, that's just a quick brain refresher for those of you who piece all that together without help.