You have underestimated the Bears supporters both in northern & greater Sydney and around Australia. Those eyeballs alone are plenty. As well as the increased spice to valid local derbies. Also think you underestimate that first he good off the code is important as well. I would suggest a decent tv partner would want to promote and see the code that it's contracted improve developmentally and in the market place. Both are achieved with Central Coast Bears with minimal infrastructure imposts. Makes good sense for prudent rugby league people and businessmen I suggest. .
How many sets of eyes are we talking here? 10k? Let's be generous and say 50k. That is not enough to get broadcasters to cough up enough to cover the cost of the bears in the NRL let alone their presence add value to the comp.
Secondly, the only derby that pulls big crowds for Norths would be manly. Andy by big crowds we are talking 20k, which is just.... ok, not fantastic. One game at 20k and the rest at 10 - 14k is not enough to help raise the league attendance average either. Yes, Perth and NZ2 wil probably average crowds like this but their ceiling for growth is much higher and they would significantly add to the value of the broadcast deal over and above the cost of having them in the league.
You know what would promote the code better than the CC Bears? A second Brisbane team (essentially extinguishing Union & AFL in Brisbane) and a Perth team (giving us a national footprint). This is attractive to broadcasters and nation-wide sponsors. A tenth Sydney club, not so much.
Brisbane 2, NZ2 and Perth also have stadia ready to roll and would require minimal infrastructure. I know you are not against the inclusion of these clubs but I point this out because this is what the bears are up against if they want inclusion and their business case just doesn't stack up.