Why didn't the Mavericks ever have 1 superstar besides Dirk Nowitzki all these years?

The last guy they had was Steve Nash, but that was a long time ago. Why didn't he even switch? Besides that Nowitzki never had one star on that team who was still in his prime? Why if so many players switch teams these days? LeBron James even joined a team filled with superstars, so it would make it easy to win rings. He expects to win 7 rings at Miami.