This is about one thing and one thing only - State of Origin. Players like Segeyaro, Milford, Papili, Uate are scared to harm their Origin chances so will reject their country every time - even if that means they will never get picked for Australia or their nation (Samoa, Tonga, Fiji).
If you made Origin rules that said you had to be living in your state before the age of 13 but could represent any country you wanted to internationally then you would find players putting their hand up for who they really wanted to play for.
Is it that difficult?