In no particular order...
1. Weather
Even in winter people are still walking around in thongs (the shoe kind BTW

)
2. Able to be mortgage-free therefore financially secure
No way would we have achieved that in the UK at our age. In fact we'd have ended up with quite a sizeable shortfall on the endowment so we would have had to downsize to pay said shortfall
3. Sun, sea and surf
Where we live the beach stretches as far as the eye can see. I'm in Seventh Heaven
4. More laid back lifestyle.
Australians are an extremely friendly bunch
5. Different opportunities
Both for us and our boys
Sorry, but must add this as well...
6. Australia is a country that enjoys political autonomy. It can create it's own policies and guidelines without the interference of anyone else therefore giving you a much freer outlook on life
Dolly