Can't speak for anyone else, but
Better Money, lower cost of living, better lifestlye, move closer to the rest of the world, see more of the family, access to leave, better rosters...the list does go on....
Unsure of whether the regulator actually would be aware of the staffing situation in Aus at the moment and any future predictions.
It is a great career, had 15 wonderful years in OZ and you have to start somewhere. If you apply yourself and work hard you will get there, the training bond is for 5 yrs (I think) but most OS places wouldn't take you on with much less experience than that anyway.
Good luck with whatever you decide.