>10% of the Kiwi population went to their culturally-similar neighbour with a much better economy. Similar story with >15% of the Irish emigrating, mostly to less-economically-dire Britain (although there's a long established Irish exodus tradition), and for that matter the >1.2 million Brits off to Australia.
I expect most of these migrations won't be permanent, and these stats probably include a large proportion on 1 year working visas.
Yeah, and a key thing missing from these graphs is ease of movement. As far as I know, Australia is about the only country Kiwis can move to for work without requiring a visa, whereas the UK is getting stricter and stricter each year as it looks towards the EU rather than the Commonwealth.
I expect most of these migrations won't be permanent, and these stats probably include a large proportion on 1 year working visas.