Chris Price:

There are many reasons:

Australia is far from the rest of the world, so when Australians get out of their country, they go for a long time and visit a lot of countries, like doing a tour around the world
There is a tradition for young Australians to take a year off at the end of their studies to go discover the world
Many Australians have relatives in the UK or in other European countries they like to visit and they visit other countries on the way on stopover
Australia is about the same everywhere and doesn’t have the deep culture and history of Asia and Europe, so it makes it interesting to travel there
Australians are rich, have 4 weeks of paid vacations plus long-service leaves, so they can afford to travel
Australia is an expensive place to travel, so it’s cheaper to travel in Asia, Latin America and even in some countries of Europe than in Australia
Australia’s seasons are reversed to the Northern Hemisphere, so Australians like to enjoy the summer in other countries when it’s winter in Australia and cool down during their long hot summer