A sidenote is that Wii actually ran a separate operating system (nicknamed IOS by the community) in a dedicated ARM processor (Starlet), that was responsible for performing the majority of device input/output, including disk access, internal and external storage, and notably in this case, networking - the TCP/IP stack was implemented entirely there.
Besides running on a weaker CPU, IOS can access (for exclusive use) some of the main system memory, but it was usually about 12-16MB to not starve the actual games running on the main CPU (https://wiibrew.org/wiki/Memory_map), which can help explain why everything except for the actual games was so slow.
Originally, code running on the main PPC CPU could not access directly most of the IO related hardware at all (only GPU/display output and wired controllers - the bluetooth stack was also on IOS AFAIK, but the Wiimote drivers themselves were userspace), so even the Linux ports had to "proxy" some hardware access through the IOS, but later after reverse-engineering the full boot process, people were able to create a replacement IOS that could enable full access through a special register: https://wiibrew.org/wiki/MINI, enabling full-speed Linux ports, and since that functionality is about a decade old now, I would guess that the NetBSD port also takes advantage of that.
Besides running on a weaker CPU, IOS can access (for exclusive use) some of the main system memory, but it was usually about 12-16MB to not starve the actual games running on the main CPU (https://wiibrew.org/wiki/Memory_map), which can help explain why everything except for the actual games was so slow.
Originally, code running on the main PPC CPU could not access directly most of the IO related hardware at all (only GPU/display output and wired controllers - the bluetooth stack was also on IOS AFAIK, but the Wiimote drivers themselves were userspace), so even the Linux ports had to "proxy" some hardware access through the IOS, but later after reverse-engineering the full boot process, people were able to create a replacement IOS that could enable full access through a special register: https://wiibrew.org/wiki/MINI, enabling full-speed Linux ports, and since that functionality is about a decade old now, I would guess that the NetBSD port also takes advantage of that.