Also the nurses and firefighters disputes are not being played out on the front page of the paper every second day, so the "public"
Incorrect. Nurses and firefighters come under the State industrial system and therefore are not subject to FWA (aka Julia's system for industrial chaos). That is why the bus drivers were able to wildcat strike last week in Sydney with impunity. That wasn't and didn't need to be PIA.
FWA provides that the government can step in in the national interest. When that test is satisfied, is only known to them.