I'm not so necessarily sure that Auckland is where its at with regards to the amateur game. Let me give you a different thought:
Auckland teams with the Premiership. This can also be born out in a saying 'Success breeds success'
Why do players move to Auckland? Cause they want to win. Why do they want to win? Cause the teams they are at do not. If Team Wellington had won 4 of the 8 seasons, would the crowds be at 200? Probably not. Would players move to Wellington to play for them? More than likely. Why do players follow Wayne Bennett? Because his teams invariably win. If a different team for the 1st time in 8 years pinches and O League spot, what do you think will happen to one of the Auckland sides?
The simple answer to all of this is that winning attracts people. 2002 basketball champs, Americas Cup wins, rugby WC, 2010 WC South Africa. Teams that win, attract spectators, followers and people that want to be involved with it.
The Phoenix are not currently successful and thus, not many people are really giving a shit and I'll refer to those as the casual observers that turn up when we are winning and no other time or those at out of town venues that can't be bothered spending cash to watch their teams get @ss raped (or people that live in Auckland and have a team in play in their own backyard)