Apart from the fact that people might not want it, even technically you might still have latency issues, our eyes are extremely sensitive… also keep in mind: the sensors and displays you need on head might still weigh a lot and consume a lot of power on your head, even if all processing power is relegated to an external unit.

Nobody would buy it. Worst that might fly is a cord going to a phone, and I'm not sure about that.

Apple decided against requiring a separate compute device. Because it sucks that’s why.