Using that logic sky could pay the nzru half what they currently doThat's precisely it.
The NZ TV market has one bidder with cash - Sky
The FTA channels either can't match them (taxpayer owned TVNZ), or aren't willing to try (TV3 owned by Discovery, but unlikely to get in a bidding war), so Sky can pretty much name their price, and FTA will be happy with whatever crumbs Sky drops their way.
Totally different dynamic to Australia, as we have no anti-syphoning laws & no current pay TV sports competitor to Sky.
an extra team is valuable to sky nz