A few people did put in some bunkers but they had to do it secretly because none of the councils would sign them off. At the time there was no regs concerning the legality of them and if you put one in the council wouldn't give you your C of Occupancy. Personally I think they are a good idea but they have to be done right.
I tend to agree, with a proviso, and risking being called a "resident expert" will offer the following.
The last paragraph of the AFACS document I linked above:
"And lastly, while on the face of it properly designed and situated fire bunkers seem to offer a failsafe,
last-resort option to residents living in bushfire-prone areas, this will not necessarily be the case. On
days like Black Saturday, it is essential that residents who are going to use a fire bunker enter it before
the fire strikes their property. The experience of the Black Saturday fires indicates that those who
attempt to defend their properties first and then seek refuge in a fire bunker may not be able to do so
for a range of reasons."