There is far more money at stake in maintaining the legitimacy of the the NBA (player salaries, tv deals, team valuations - all of these easily trump all the money made off of betting). Wouldn't that money fight a lot harder than any bent refs in order to fight corruption and maintain the legitimacy of the NBA?
If a bigger story about bent refs got out it would destroy the NBA and a lot of the associated revenue. I'm sure the NBA is aware of this.
I'm not arguing that there is no corruption, but I don't see why it's so 'obviously' commonplace as you and others suggest. I'd like a more concrete reason why than 'its good for marketing' since that seems like a weak argument in the bigger picture of money made from the NBA.