It's a beautiful area, like the Gold Coast and Perth. I just don't think Sutherland has enough people to support an NRL team. Its population is less than 250k, making it around the size of Ipswich. There's no team in Ipswich.
Logan has around 330k, produces more NRL talent than Sutherland and is arguably the most parochial rugby league region in Australia, yet it doesn't have a team. There are plenty of affluent suburbs in Logan, too, but I don't see people rallying for a team based on that reason alone. There's no way Logan will get a team of its own because it would be sandwiched between Broncos and Titans, but for that reason Sharks shouldn't be in the NRL.
If Sharks were to represent all of Southern Sydney and Illawarra then they would be strong and a valuable asset to the NRL, but they don't and cannot while the Dragons are in the competition and have them sandwiched into Sutherland.