Well, the salary cap portion of the Nix expenses is funded by TV revenue, but the club has a lot of other expenses to meet and publicly announces losses year on year. Every year we hear that the failure to break even on match days is a major contributor to those loses. We also lag in absolute numbers (though not relative numbers) compared to most of the Australian teams. Because our presence in the league is seen as tenuous, any excuse to suggest we're on the way out will be taken by the media (and some fans).
The six major cricket associations get their money from NZC, pokies, and other sponsorship. Gates don't matter. In fact the Firebirds would do well to see 1500 people across 10 Plunket Shield games this season. People haven't gone to domestic cricket in significant numbers for a long time and that is why the T20s are organsied directly in the interests of TV viewers this season (though a bit of money is probably saved on travel, which would be welcomed given that while they survive, they are still tight budgets).
Basically, our club's owners go around saying that the crowds aren't good enough and we can't survive like this long term, while if domestic cricket is about to go under, they're being very quiet about it. So low Nix crowds are a story, low cricket crowds are not.