Kaz. If it was that simple why wouldn’t other countries mark the atc frequency boundaries on charts so that their controllers would have the duty of care to call non participating VFR aircraft and tell them they are close to other aircraft?
Now think about it? Any idea?
A hint. Most likely it would reduce safety as it would dilute responsibility- “no need to remain vigilant because I’ll get called by a friendly ATC.”
And it simply doesn’t work. For example the riskiest place for mid airs would be in the Bankstown training area. Yet in all my flying career I have never heard ATC make the obvious call. “ VFR aircraft near Waragamba Dam. - turn left. You are about to collide with another VFR aircraft “
So if you go flying in G airspace with the hope that an ATC will randomly call you to prevent a collision you are delusional and should see you doctor!