In order to become a star player, a team sort of needs to have the right amount of talent (or lack of it) in the right places.
Steve Nash doesn't average 11apg if he's sharing the court with a bunch of playmakers. In his 2004-2005 MVP season, the next best assist guy was Joe Johnson, at 3.5apg. Most of the others were well known finishers/spot up shooters.
If Nash is surrounded by playmakers, he ends up being the defacto spot shooter.
Johnson left the Suns the following year and averaged 6.5apg with the Hawks that season, earning an all-star spot. He also left a playmaking void on the Suns. Without JJ, Steve Nash took even more of a hold on offense, earning his 2nd MVP award.
Brunson was stuck behind an MVP candidate. He basically had to adapt his game to make it as an undersized SG in order to earn minutes. I think that says something about his resolve to earn minutes, help his team, AND earn a big contract.