It was recently reported that john Corzine spent 130 million of his own money in his last three election campaigns. Why would anyone spend that much money to get a job that only pays a couple hundred thousand a year?
The only thing I can think of that would make someone with that much money getting into politics is the fact that they can get into the position of power to help push their agenda. For example, he was a big time universal health care, gun registration, mandatory public preschool, affirmative action, same sex marriage guy......along with several other things. He could either vote, support and donate to a candidate with his views or get into politics himself, which he did. For a lot of them it is about the power and connections they have and can make to push their agenda on others.
I don't think he was doing it for the good of the people. His career in banking and finance made him enough money that he probably lost touch with reality like many politicians do.