I'm not involved on either side but my impression is that most Australian landlords aren't inherently nasty or greedy.
However with a large number of mum-and-dads owning investment properties (often with interest-only high-LTV home loans), they have to raise rents to cope with current interest rates. True, negative gearing can cushion the blow but only up to 48%
Once the new market rate has been set, other landlords are obliged to follow (for new tenants at least)
Low housing stock means standard economic market forces don't apply
(Even worse, rent is included in the CPI so high interest rates lead to rental inflation lead to ongoing high interest rates in a vicious circle)