CP has consistently been injured when the Sun's need him in the playoffs and is only getting older. Terry Rozier is a younger PG who has been in the playoffs before. He is not a true point guard but he has some experience at that position and will find it much easier when sharing the ball with Booker and Durant.
Charlotte will get off Paul's contract after one season since it's non guaranteed. CP can also hopefully teach Melo (and Scoot) how to defend.