I think you don't have to look to far past ASA to find the reason WAAS hasn't happened. It's the same reason why it hasn't happened in this side of the Tasman either. ASA and Airways NZ haven't found a way to obtain revenue from WAAS or other SBAS systems as they are basically free to air, plus as has been mentioned the big guys don't need it.
How many dollars did ASA spend on their GBAS system that they tried to develop with Honeywell.
Ground Based Augmentation System | GBAS |
What happened to this? Was supposed to be up and running in 2009.
I suspect their motivation for such a system is so that they can develop a revenue stream out it.