That’s because they are concerned police will have a speed trap in the lane.
If there were a requirement for vehicles in the “slow lane” to reduce their speed by 10km/h or an allowance for overtaking motorists to momentarily speed — as is already happening by 85% of users — more vehicles could pass.
That would lead to reduced risk-taking and road rage.
There are fines for this sort of behaviour. In Queensland, motorists can cop a $76 fine and two demerit points for driving in the right lane without overtaking in areas with 90km/h or higher speed limits, including passing lanes.