WiFi routers kind of inherently need to do a lot: 1. Drivers for wifi & ethernet ports, and other hardware needed for the device. 2. TCP stack and routing mec

WiFi routers kind of inherently need to do a lot: 1. Drivers for wifi & ethernet ports, and other hardware needed for the device. 2. TCP stack and routing mechanisms for forwarding packets between the two. 3. Access control for wifi portion, which (depending on how much flexibility is needed) may involve keeping track of individual user accounts and permissions. 4. Some way to administer this complexity. Currently the only thing that seems to fly with users is a web administration interface. 5. All the "usual" OS stuff to manage this: process scheduler, filesystem layer, memory management, etc. Sure, you could design a special purpose OS that's simpler than Linux, but the development effort required would be much higher, and it's not clear to me that you'd end up with something much more bug-free.