Final answer:
George felt compelled to walk on Trunion Pike due to his strong desire to see his wife and children, which gave him the resolve to push through fatigue and hunger.
Step-by-step explanation:
The main reason George had the urge to walk on Trunion Pike on the morning of his departure was the overwhelming desire to reunite with his family. This emotional urging is highlighted by the mention that by nightfall he was fatigued, footsore, and famishing, yet the thought of his wife and children propelled him forward.
It's the anticipation of rejoining his loved ones that guides his determination and directs his steps to traverse the wide and straight, yet seemingly untraveled road that led him in what he believed to be the right direction towards home.