You asked "why" people would "move"? The main reason I used to "move" was my locals were all SD and they were visually horrible. Why would I watch network TV in crappy SD on my gigantic HDTV when there was a signal already coming to my house in beautiful HD? Like others have said, Directv doesn't care and/or are indifferent as long as you are paying.
My locals are still horrible stations, but they are in HD now, so I "moved" back.
My locals are still horrible stations, but they are in HD now, so I "moved" back.