I don't understand why people work ridiculously long and hard hours in Wall Street or the City for more money than they could ever use.

My brother works long hours on Wall Street. He says that most people in finance retire significantly earlier than the rest of the population. He also says that people working in finance generally value money more than time, and that this is a self-reinforcing system. People not willing to work long hours for a high hourly rate don't find the jobs attractive, and the people already hired prefer not to have extra help; the money to hire each extra person would, essentially, come directly out of their own salaries.