By that logic, why should rich people ever take risks at all? Aren't they already rich?

I'd say it was a pretty smart move on his part. Conspiracies don't get revealed by the straw that breaks the camel's back anyway, the camel is already buried in a mountain of straw, the trick is finding the needle... I've mixed my metaphors. But you get the point. Considering he's sitting pretty, greedily taking that seventh box of money was the optimal move.