Honestly it could still be fear, at first I imagined it would be just his good heart or something but I honestly think that it could be fear. This is not just few million dollars, it is not smaller, it is 600 million dollars and when you steal that much money then it becomes a big trouble for you, not just getting it out because you will never getting it out to a normal bank and live with 600 million dollars, nobody in the world would allow you to do that, not even Deutsche bank who launders money from mafia, so that means that money is stuck with you and you can't spend all of it.
However I believe it is more than that, it is the fear of constantly looking behind your back to see if anyone is out to get you, that fear is not something anyone would want for a life time.
Honestly,it wouldn't really be that a problem because you wont really be needing for it to be bulk or one time transaction if you do really intent to have lots of money and as a hacker then that wouldn't
really be a problem since he can sustain himself.
It is just he had done just ethical and not all hackers are really that bad and some of them are white-hat which do consider out on making good things if they do know that its for the own
good of its investors or people involved.
Not all things can be bought by money.