Same as Canada. I assumed it was market forces but no, it is regulated this way! Seems like a bizarre plan to make your populace less resilient to rate fluctuations.
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.