I am at once in awe and jealous of the kinds of things these people must know/be able to do. It's too bad that this kind of skill and knowledge could not be used in a more legitimate manner with such a high profit potential to the individual.
Who says it isn't being used in a legitimate manner for high profit potential? It seems you can offer up subscriptions to zero days for millions in annual fees and never have to worry about prosecution. Just so long as you aren't the one doing the actual hacking (your clients in the government will take care of that).
I would not doubt if they got paid handsomely (if not, relatively well).