I think the OP is asking why work sixteen hour days when one can work less and still earn a living, though not as much.
Many of these Wall Street workers are highly opportunistic, highly individualistic, money-obsessed people. They spend little time with friends and family and they don't get involved with women seriously, or if they do, it's an "arrangement" of sorts. It's hard to be a good dad or partner when one works those hours. Many of them also see those with less money as being "losers" or "ordinary people". The whole thing is part of their personality, getting one up on the next person.
Money does make them happy, not just the amount one needs to lead a satisfying life, but the amount of money that makes one rich. Also, what makes one person happy might not make another person happy.