Money and happiness are two completely different things and I don't know why people try and link the two.
Why should money bring happiness? Turn it on its head and you'll see how ridiculous the notion is - ask will more happiness bring more money? Not necessarily.
There are happy poor people, happy rich people, sad poor people and sad rich people. It's very hard to correlate financial status and state of mind, they are unrelated as far as I'm concerned.
Going back to the original question - I'm sure there are people working on Wall Street doing 16 hour days purely because they want to and because they can, simple as that - it gives them purpose, it pays the bills, it's a living, it's a status thing, all of the above.