Friendly tip: please don’t use pejorative words like “garbage” when reporting an issue to open-source maintainers.
As you’ve noticed, OSRM’s default foot profile avoids trunk roads. This is because, in large parts of the world, highway=trunk is used to mean a road on which people aren’t permitted to walk.
If you’re setting up your own instance of OSRM, and you just want to run it for NZ, this is pretty easy to fix. Simply edit foot.lua and add trunk (and trunk_link) to the list of permissible highway types.
Alternatively, you can tell OSRM to use different defaults for different regions. Using location dependent data in profiles · Project-OSRM/osrm-backend Wiki · GitHub is a high-level overview of how that works.
Adding location polygons to the OSRM repo so that everyone got this out-of-the-box would be an interesting challenge and not one anyone has yet taken on!