They can't share that information as they will be found out to be either rorting the cap or get paid waaaaay too much for the way they play.
Yep. In a sport without a cap the fans don't seem to give a shit how much a player earns. Yeah sure he's overpaid/underpaid. It's just a financial detail, unrelated to competitiveness. Under a salary cap, every dollar a player gets paid is one less dollar that could go to anyone else in the squad.
Theoretically, it's the same without a cap, instead detracting from a club's budget. But if budgets are different for every club, merkins accept they will be spending different amounts on players anyway. Whether someone is on overs or unders is far less relevant than the fact it's not an even playing field in the first place. The NRL's problem is that it's not an even playing field but the existence of the cap fools merkins into thinking it is, and if their club is underperforming there must be someone to blame.