It's not that far fetched of an idea. The civilization on the moon is far from developed -- there is only one city, and the large majority of people who live there came to start a new life. If you live on the moon, the general idea is that you came to be successful -- to take your life in your own hands, and make something with it. Of course, that isn't always the case. The main character is one of the first "moon-bred" kids who grew up in one of the poorer parts of the moon. He looks at the poor people around him and hates it -- he hates how all these people came to the moon and did absolutely nothing with their life. On the other hand, when he looks at the big city, he sees exactly what he wants to achieve in life. He ends up running away from home and starts focusing on the stock markets to achieve this success -- so he can live amongst the "successful" people. So, the two concepts basically go hand in hand. The moon is the "frontier of mankind" and has many successful businesses, so it's only natural that the stock market would be important there.