Why do you think most ex convicts preferred to stay in Australia instead of returning to Britain?

Their business and family

Explanation:

After gaining their freedom, ex convicts in Australia started a new life in that country. They started to form personal relationship with one another, gaining friends and family. They also start to utilize local resources and building up their own economy.

If they leave Australia to move to Britain, they have to leave all of those behind. Most of them believe that their life was better off if they stay in Australia.