Mortgages in NZ are typically fixed for between 1 and 5 years, with most fixing around 3 years. So 95% of mortgages will always be rate adjusted in the next 3 years.
Freddie Mac and Fannie Mae or whatever they are/were take those mortgages and basically convert them into government bonds that are then sold out.
Otherwise getting 2% for 30 years would be nearly impossible (and it IS impossible in many countries).
It isn't competitive (9.75% vs 6.2% on a 5 year), but it's there.