I can't speak for switches. BUT, for me, I have always wanted to be submissive. I desire to be controlled. For a dominant, they like control and desire to be in control (from my understanding). For switches, as I have become to understand, they are submissive to some and feel dominant to another OR they wish to play the part of a submissive or dominant in a scene and then take the role of the opposite in another scene. (I hope you understand what I am saying.)