Loved the movie , one question. (SPOILER)

I think he does it because it's all he has left. It gives him a sense of still being good at something (Like he said "I was back, doing what I do best")and that he hasn't lost everything in his life.

Its his addiction. He is addicted to what he does best and also throughout the movie he mentions the feeling of being invincible. In a sense he was high on his invincibility and scared to try something new and versatile. So in the end he had reached a stage in his life where he was invincible and when the government, rebel forces and powerful corporations backing you who can stop you? Seriously, you are the door to door salesman that everyone loves and adore.

It's his ego. By the time he realized that his family was important he lost them, and had nothing left but his job which he realizes is immoral. But he won't kill himself, so he'll just keep on doing what he does best because he wants to feel big.

At the end of the day, the human being in him still yearns for the big life and he's still in the position to attain and retain it.

Look at Hollywood. There are some very fine examples of people who have traded in their family, etc for a life of luxury and excess.