Quote from Ghost of Cutten:
I don't think you understand their motivations. They are not working so they have more money to spend.
Someone who works not for the enjoyment of their work, but merely to get spending money, is never going to become a billionaire in the first place. To become a billionaire you need to love what you do for a living. Hence, even if they had $1 trillion dollars, they'd still work.
Money is not valid as the sole reason to work, unless you are struggling to put food on the table and a roof over your head. Once you have got beyond day to day survival, satisfaction is the main reason to choose a career path.