Citizenship is pretty arbitrary though. Some countries will make someone a citizen overnight so they can compete for them at the Olympics.
Some countries allow dual citizenship (mostly Commonwealth countries), others don't.
It's actually harder and less common for New Zealanders to become citizens of Australia than for many other countries because they don't need to and can stay here forever without a visa. They don't need to become a permanent resident either.
I can certainly see why most sports including rugby don't include citizenship as a qualification criteria because it would create an uneven playing field because the rules are different in different places.
