Why doesn't Nash just come to Dallas?

Once we retain Butler and Chandler, we'll have some good pieces to offer Phoenix. Nash deserves to win a ring, and what better than to join his old teammate Dirk and his old team the Mavericks all over again. He may be old, but he can still ball as he did last season. He'd be a great PG for us to run the floor with, setting up the sick pes and dunks and whatnot. Him and Kidd split time with Kidd off the bench. They're both old and will take time coming in and out. We'll have an even better chance to repeat with Nash, although we don't need him, but he'll be a great add. What are your thoughts on this?