On an individual basis the Broncos are the club that generate the largest portion of the money, after that Melbourne, NZ, and a couple of the larger Sydney clubs, after that it gets hard to tell, but your average regional club is bringing in more than the smallest of Sydney clubs.
You do realise that most backers/owners don't actually make money in professional sport right?
Do you think that the owners and backers of Sydney clubs are only in it to siphon funds from the NRL as well? Like is Rusty sitting in some office moving money from Souths bank accounts to a secret Swiss bank account as we speak? lol.
People buy/support sports clubs for all sorts of reasons, the vast majority don't get rich doing it, in fact they normally lose a fortune doing it, but some do get kick backs in the form of being able to use the team as a vehicle to advertise their products and other businesses, but a lot do indeed own/support clubs simply because they want a local team and/or for it to do well, or because they want the prestige of being able to say they own a team and are on the inside.
BTW, who do you support.