Why executives risk their jobs to tip a hedge fund

A hedge fund manager worth $1.5 billion was arrested on Friday, along with five executives who allegedly helped that hedge fund make $20 million. This raises some interesting questions.

Why would someone worth more than a billion risk it all for a little extra change? Why would executives who are probably worth millions risk their careers to help that hedge fund make a bit of extra money? Is the hedge fund in question alone in using inside information to profit?