That's because they are American locos imported here, along with their systems.
Some locos are built here using american running gear.
This has always been the Australian way of doing things. Why reinvent the wheel?
Today we still run F7 type locos built here under licence.
They keep getting refurbished and put back to work.
They do the job because our trains tend to be a lot smaller than in the US.
Cheers,
Mike