Interesting.
My daughters and I were talking about this kind of thing last weekend, but we were talking about movie stars (and musicians) who make $$$$$$$ for one movie. We agreed that we don't see why they'd ever bother to make a 2nd, 3rd, or 4th movie -- not when they've already earned enough for their children's children to be wealthy! We agreed that it must be about the "need" for fame and popularity and the desire to stay in the limelight rather than fade away. After all, from a practical point of view, even if the work were easy and fun, doing whatever you please is always more easy and fun.
I suppose people like stock brokers could experience this same kind of thing -- rather than needing the money, they want to command more and more power, more and more "wins". It's a different faucet of the same idea.