Probably because the airspace had little to do with at least two of them. Take them out and you've had two accidents in 16 years that you allege were airspace related, but involved completely different circumstances. Hardly reason for wholesale change.
Re Benalla 2004
"The investigation found that instructions to controllers relating to RAM alerts could be ambiguous. Actions taken by Airservices Australia to enhance alerts and clarify controllers' responses to them, should avoid a recurrence."
It would appear to have done so.