Except they don't sign up for privacy violations. They sign up to make music, or act in films, or whatever it is they do.

I'm sure some famous people purposefully encourage paparazzi to follow them, but certainly not all of them. You must have noticed how most of the photos coming from paparazzi feature someone who's famous in particular circles looking pissed off at a gaggle of photographers following them around as they go to the shops with a hangover.