Because they're close to the city?
Look at a map of Sydney and point out to me where Marrickville and North Sydney are dude.
So theoretically, Roosters could become the biggest team on the North Shore within a couple of generations by marketing themselves better to the region's children, yeah?
Anyone born after 2000 wouldn't give a f**k about the Bears. They never saw them play so they have no emotional attachment. No reason why they cannot become avid Roosters fans. Just need to get the Roosters to get their attention. We've got a great game and onionball is on death's door, so no excuse for us not to become number one on North Shore. When the kids grow up they'll be able to travel to SFS to see the Roosters play 12 times a year.
South Melbourne relocated to Sydney in the early 80s. A generation later, around the late 90s, their attendances grew. The same thing can happen for the Roosters on the North Shore.
You mentioned Newtown and Balmain. That's Inner West. If people from the Inner West can get to the SCG to warch the Swans play fumbleball then there's no reason the Bulldogs and Tigers cannot get people from this region to travel to the SFS.